To reproduce: Add a Drums contraption. Add any contraption that has combo-boxes in it (for example Bassline). Place the Bassline over the Drums, so that one of the combo-boxes is positioned over the Drums' pattern editor. Press play. Move mouse cursor over the combo-box and wait. When the vertical line that runs through the Drums moves underneath the bassline combo-box while the cursor is positioned over it, it leaves weird green dots visible around the combo-box :)
Happens on a Lenovo notebook with Sandy Bridge intergrated graphics (HD3000), Windows 7.
Oops, I meant Arpeggiator, its 4 combo-boxes make it much better visible, but also happens with Bassline.
Screenshot:
http://img651.imageshack.us/img651/4827/mulch.jpg
I see the same thing, on a Mac. Now showing up on Windows, too, eh?
I described it here, fyi:
http://www.audiomulch.com/content/green-fur-mac-gui
Thanks for reporting this and for providing such a clear description of how to reproduce it.
This should be resolved for the 2.2 release, although it isn't fixed in the current Alpha versions, it should be fixed in the Beta series.