diff --git a/src/db/unit_tests/dbAsIfFlatRegionTests.cc b/src/db/unit_tests/dbAsIfFlatRegionTests.cc
index 2e97ac6b8..31377c2c2 100644
--- a/src/db/unit_tests/dbAsIfFlatRegionTests.cc
+++ b/src/db/unit_tests/dbAsIfFlatRegionTests.cc
@@ -1663,14 +1663,17 @@ TEST(40_BoolWithProperties)
   db::RecursiveShapeIterator si1 (ly, top_cell, l1);
   si1.apply_property_translator (db::PropertiesTranslator::make_pass_all ());
   db::Region r1 (si1);
+  r1.set_join_properties_on_merge (false);
 
   db::RecursiveShapeIterator si2 (ly, top_cell, l2);
   si2.apply_property_translator (db::PropertiesTranslator::make_pass_all ());
   db::Region r2 (si2);
+  r2.set_join_properties_on_merge (false);
 
   db::RecursiveShapeIterator si3 (ly, top_cell, l3);
   si3.apply_property_translator (db::PropertiesTranslator::make_pass_all ());
   db::Region r3 (si3);
+  r3.set_join_properties_on_merge (false);
 
   db::Layout target;
   unsigned int target_top_cell_index = target.add_cell (ly.cell_name (top_cell_index));
@@ -1802,6 +1805,7 @@ TEST(41_EdgesWithProperties)
   db::RecursiveShapeIterator si2 (ly, top_cell, l2);
   si2.apply_property_translator (db::PropertiesTranslator::make_pass_all ());
   db::Region r2wp (si2);
+  r2wp.set_join_properties_on_merge (false);
   db::Region r2wp_nomerge = r2wp;
   r2wp_nomerge.set_merged_semantics (false);
 
@@ -1846,12 +1850,14 @@ TEST(42_DRCWithProperties)
   db::RecursiveShapeIterator si1 (ly, top_cell, l1);
   si1.apply_property_translator (db::PropertiesTranslator::make_pass_all ());
   db::Region r1 (si1);
+  r1.set_join_properties_on_merge (false);
   db::Region r1_nomerge (r1);
   r1_nomerge.set_merged_semantics (false);
 
   db::RecursiveShapeIterator si2 (ly, top_cell, l2);
   si2.apply_property_translator (db::PropertiesTranslator::make_pass_all ());
   db::Region r2 (si2);
+  r2.set_join_properties_on_merge (false);
   db::Region r2_nomerge (r2);
   r2_nomerge.set_merged_semantics (false);
 
@@ -2000,10 +2006,12 @@ TEST(44_SizeWithProperties)
   db::RecursiveShapeIterator si1 (ly, top_cell, l1);
   si1.apply_property_translator (db::PropertiesTranslator::make_pass_all ());
   db::Region r1 (si1);
+  r1.set_join_properties_on_merge (false);
 
   db::RecursiveShapeIterator si2 (ly, top_cell, l2);
   si2.apply_property_translator (db::PropertiesTranslator::make_pass_all ());
   db::Region r2 (si2);
+  r2.set_join_properties_on_merge (false);
 
   db::Layout target;
   unsigned int target_top_cell_index = target.add_cell (ly.cell_name (top_cell_index));
@@ -2017,6 +2025,10 @@ TEST(44_SizeWithProperties)
   target.insert (target_top_cell_index, target.get_layer (db::LayerProperties (20, 0)), r2.sized (200));
   target.insert (target_top_cell_index, target.get_layer (db::LayerProperties (21, 0)), r2.sized (250, 50, 2));
 
+  r2.set_join_properties_on_merge (true);
+  target.insert (target_top_cell_index, target.get_layer (db::LayerProperties (30, 0)), r2.sized (200));
+  target.insert (target_top_cell_index, target.get_layer (db::LayerProperties (31, 0)), r2.sized (250, 50, 2));
+
   CHECKPOINT();
   db::compare_layouts (_this, target, tl::testdata () + "/algo/flat_region_au44.gds");
 }
diff --git a/src/db/unit_tests/dbRegionTests.cc b/src/db/unit_tests/dbRegionTests.cc
index da2c12249..04b3dc90b 100644
--- a/src/db/unit_tests/dbRegionTests.cc
+++ b/src/db/unit_tests/dbRegionTests.cc
@@ -2069,11 +2069,17 @@ TEST(50_PropertiesFlat)
     "{}:(10,20;10,220;110,220;110,20)"
   );
 
+  r.set_join_properties_on_merge (false);
   EXPECT_EQ (sip2s (r.begin_merged ()),
     "{id=>1}:(1,2;1,202;101,202;101,2)\n"
     "{id=>42}:(11,12;11,212;111,212;111,12)\n"
     "{}:(0,0;0,200;10,200;10,220;110,220;110,20;100,20;100,0)"
   );
+
+  r.set_join_properties_on_merge (true);
+  EXPECT_EQ (sip2s (r.begin_merged ()),
+    "{id=>42}:(0,0;0,200;1,200;1,202;10,202;10,220;110,220;110,212;111,212;111,12;101,12;101,2;100,2;100,0)"
+  );
 }
 
 //  "+" operator with properties (issue #1373)
@@ -2165,11 +2171,17 @@ TEST(51_PropertiesFlatFromLayout)
     "{}:(10,20;10,220;110,220;110,20)"
   );
 
+  r.set_join_properties_on_merge (false);
   EXPECT_EQ (sip2s (r.begin_merged ()),
     "{id=>1}:(1,2;1,202;101,202;101,2)\n"
     "{id=>42}:(11,12;11,212;111,212;111,12)\n"
     "{}:(0,0;0,200;10,200;10,220;110,220;110,20;100,20;100,0)"
   );
+
+  r.set_join_properties_on_merge (true);
+  EXPECT_EQ (sip2s (r.begin_merged ()),
+    "{id=>42}:(0,0;0,200;1,200;1,202;10,202;10,220;110,220;110,212;111,212;111,12;101,12;101,2;100,2;100,0)"
+  );
 }
 
 TEST(52_PropertiesDeep)
diff --git a/testdata/algo/flat_region_au44.gds b/testdata/algo/flat_region_au44.gds
index 2484aecb1..daf5df77d 100644
Binary files a/testdata/algo/flat_region_au44.gds and b/testdata/algo/flat_region_au44.gds differ
diff --git a/testdata/ruby/dbRegionTest.rb b/testdata/ruby/dbRegionTest.rb
index f5dc08881..761fa65a7 100644
--- a/testdata/ruby/dbRegionTest.rb
+++ b/testdata/ruby/dbRegionTest.rb
@@ -1636,8 +1636,13 @@ class DBRegion_TestClass < TestBase
     r.insert(RBA::Box::new(10, 20, 110, 220))
     s = r.each.collect(&:to_s).join(";")
     assert_equal(s, "(10,20;10,220;110,220;110,20) props={};(0,0;0,200;100,200;100,0) props={1=>one}")
-    s = r.each_merged.collect(&:to_s).join(";")
+    rr = r.dup
+    rr.join_properties_on_merge = false
+    assert_equal(rr.join_properties_on_merge, false)
+    s = rr.each_merged.collect(&:to_s).join(";")
     assert_equal(s, "(10,20;10,220;110,220;110,20) props={};(0,0;0,200;100,200;100,0) props={1=>one}")
+    s = r.each_merged.collect(&:to_s).join(";")
+    assert_equal(s, "(0,0;0,200;10,200;10,220;110,220;110,20;100,20;100,0) props={1=>one}")
 
     r = RBA::Region::new
     r.insert(RBA::BoxWithProperties::new(RBA::Box::new(0, 0, 100, 200), { 1 => "one" }))
@@ -1654,6 +1659,8 @@ class DBRegion_TestClass < TestBase
     r.insert(RBA::PolygonWithProperties::new(RBA::Box::new(0, 0, 100, 200), { "one" => -1 }))
     r.insert(RBA::PolygonWithProperties::new(RBA::Box::new(1, 1, 101, 201), { "one" => 17 }))
     r.insert(RBA::PolygonWithProperties::new(RBA::Box::new(2, 2, 102, 202), { "one" => 42 }))
+    r.join_properties_on_merge = false
+    assert_equal(r.join_properties_on_merge, false)
 
     assert_equal(r.filtered(RBA::PolygonFilter::property_filter("one", 11)).to_s, "")
     assert_equal(r.filtered(RBA::PolygonFilter::property_filter("two", 17)).to_s, "")
@@ -1666,6 +1673,16 @@ class DBRegion_TestClass < TestBase
     assert_equal(csort(r.filtered(RBA::PolygonFilter::property_glob("one", "1*")).to_s), csort("(1,1;1,201;101,201;101,1){one=>17}"))
     assert_equal(csort(r.filtered(RBA::PolygonFilter::property_glob("one", "1*", true)).to_s), csort("(2,2;2,202;102,202;102,2){one=>42};(0,0;0,200;100,200;100,0){one=>-1}"))
 
+    rr = r.dup
+    rr.filter(RBA::PolygonFilter::property_filter("one", 17))
+    assert_equal(csort(rr.to_s), csort("(1,1;1,201;101,201;101,1){one=>17}"))
+
+    r.join_properties_on_merge = true
+    assert_equal(r.join_properties_on_merge, true)
+    assert_equal(csort(r.filtered(RBA::PolygonFilter::property_filter("one", 42)).to_s), csort("(0,0;0,200;1,200;1,201;2,201;2,202;102,202;102,2;101,2;101,1;100,1;100,0){one=>42}"))
+
+    # deep regions
+
     ly = RBA::Layout::new
     top = ly.create_cell("TOP")
     l1 = ly.layer(1, 0)