Candidate for fix.

src/pya/pya/pyaObject.cc

@@ -306,7 +306,11 @@ PYAObjectBase::detach ()
       }
     }
 
-    detach_callbacks ();
+    //  NOTE: m_owned = false might mean the C++ object is already destroyed. We must not
+    //  modify in this case and without is_managed() there is no way of knowing the state.
+    if (m_owned) {
+      detach_callbacks ();
+    }
 
     m_obj = 0;
     m_const_ref = false;

src/rba/rba/rbaInternal.cc

@@ -402,7 +402,11 @@ Proxy::detach ()
     }
   }
 
-  clear_callbacks ();
+  //  NOTE: m_owned = false might mean the C++ object is already destroyed. We must not
+  //  modify in this case and without is_managed() there is no way of knowing the state.
+  if (m_owned) {
+    clear_callbacks ();
+  }
 
   m_self = Qnil;
   m_obj = 0;

testdata/ruby/basic_testcore.rb

@@ -1402,6 +1402,12 @@ class Basic_TestClass < TestBase
       a._manage
     end
 
+    # Looks like Ruby is keeping the last A instance in some kind of cache:
+    # this will release it
+    a = RBA::A.new
+    a._destroy
+    a = nil
+
     # makes sure the objects inside the block before are deleted
     GC.start