infact this is not really a bug, irrespective zero vertex group weights gave overlapping geometry which isn't useful, add an option to set the thickness factor for zero weighted verts.
from the current shape mix. The old behavior is still accessable from the
menu as "New Shape From Mix".
Checked with Sergey and Bassam that this is a good change. New users
expect the add shape button to simply add a new blank shape, and get
confused when that is not the case. It is also really easy to
accidentally have other shape information in a new shape when the
"from mix" behavior is default.
ui/ --> startup/bl_ui
op/ --> startup/bl_operators
scripts/startup/ is now the only auto-loading script dir which gives some speedup for blender loading too.
~/.blender/2.56/scripts/startup works for auto-loading scripts too.