Phantoms when I move the cursor in Gtk apps

[Stefan Monnier <monnier@iro.umontreal.ca>]

In text areas with a cursor (e.g. editing boxes in Firefox), as I move the
cursor, the old location of the cursor is apparently not properly undrawn,
leaving me with phantom cursors.  See attached image.

Has anyone seen something like that?  This is on one of my Debian
"testing" systems.  I have two other "testing" systems (originally installed
at different times, but with fairly similar configurations) and those don't
exhibit this behavior.

I've tried to compare the list of packages installed but couldn't find
any relevant difference.


        Stefan