fixes #211. +/++ only clear scalaVersion/scalaHome in Global config+task.

main/Cross.scala

@@ -6,7 +6,7 @@ package sbt
 	import Keys._
 	import complete.{DefaultParsers, Parser}
 	import DefaultParsers._
-	import Project.Setting
+	import Project.{ScopedKey, Setting}
 	import Scope.GlobalScope
 
 object Cross
@@ -33,7 +33,10 @@ object Cross
 		Project.setProject(session, newStructure, command :: state)
 	}
 	def crossExclude(s: Setting[_]): Boolean =
-		s.key.key == scalaVersion.key || s.key.key == scalaHome.key
+		s.key match {
+			case ScopedKey( Scope(_, Global, Global, _), scalaHome.key | scalaVersion.key) => true
+			case _ => false
+		}
 
 	def crossParser(state: State): Parser[String] =
 		token(Cross <~ OptSpace) flatMap { _ => token(matched( state.combinedParser & spacedFirst(Cross) )) }

sbt/src/sbt-test/actions/cross/build.sbt

@@ -0,0 +1,18 @@
+scalaVersion in ThisBuild := "2.7.7"
+
+scalaVersion := "2.9.1"
+
+scalaVersion in update <<= scalaVersion {
+  case "2.9.1" => "2.9.0-1"
+  case "2.8.2" => "2.8.1"
+  case x => x
+}
+
+InputKey[Unit]("check") <<= inputTask { argsT =>
+  (argsT, scalaVersion in ThisBuild, scalaVersion, scalaVersion in update) map { (args, svTB, svP, svU) =>
+    def check(label: String, i: Int, actual: String) = assert(args(i) == actual, "Expected " + label + "='" + args(i) + "' got '" + actual + "'")
+    check("scalaVersion in ThisBuild", 0, svTB)
+    check("scalaVersion", 1, svP)
+    check("scalaVersion in update", 2, svU)
+  }
+}

sbt/src/sbt-test/actions/cross/test

@@ -0,0 +1,3 @@
+> check 2.7.7 2.9.1 2.9.0-1
+> ++ 2.8.2
+> check 2.8.2 2.8.2 2.8.1