Marcel Taeumel uploaded a new version of Morphic to project The Trunk:
http://source.squeak.org/trunk/Morphic-mt.1336.mcz

==================== Summary ====================

Name: Morphic-mt.1336
Author: mt
Time: 10 May 2017, 10:13:26.142647 am
UUID: 4d60356c-2429-724c-9d45-4fe22cd330fc
Ancestors: Morphic-ul.1335

Quick fix to avoid accidential drops of system windows into the world main docking bar.

Actually, we should think about the necessity of having the preference #systemWindowEmbedOK, which is set to "true" in current images. Setting that preference to "false" would have also solved the issue but committing state (other than code) via Monticello is cumbersome.

I think that that preference origins from the time when we could manage worlds in worlds and also MVC windows having Morphic worlds. Much of that code was removed in the course of clean-up since MVC and Morphic are quite different in their basic event processing and drawing methods.

=============== Diff against Morphic-ul.1335 ===============

Item was changed:
  ----- Method: SystemWindow>>wantsToBeDroppedInto: (in category 'events') -----
  wantsToBeDroppedInto: aMorph
  	"Return true if it's okay to drop the receiver into aMorph"
+ 	^ (aMorph isWorldMorph or:[Preferences systemWindowEmbedOK])
+ 		and: [aMorph isDockingBar not]!
- 	^aMorph isWorldMorph or:[Preferences systemWindowEmbedOK]!