It seems that the changes in area.c ("Changed order of keymaps... the
default maps now are evaluated *after* the own custom maps, so you can
make overrides or defaults.") have broken some default
Namely, it is now impossible to use Grease Pencil anywhere, because
the all operators mapped to LeftMouse gobble any event containing the
left-mouse, even if they can't do anything with them at the time. For
example, in 3D-View, this is the Set Cursor operator, and in the Image
Editor, this is the sample colours operator. Probably both of these
should not be ignoring the DKEY modifier that is used in conjunction
with LeftMouse to draw though...
I'm currently still checking if there are other broken tools around
the place, but probably there aren't many others.