bug#6739: 24.0.50; hang in *VC-log* -- redisplaying?

[rogers-emacs]

   In emacs built from git on 17-July (on openSUSE GNU/Linux 11.0), I am
experiencing frequent hanging in *VC-log* buffers.  In a fresh *VC-log*
buffer, as soon as I type "SPC RET", the cursor disappears and I get no
response.  Typing C-g restores control, though sometimes I have to C-g
twice or more.  It appears to be a display problem, as the display
updates to reflect keystrokes typed before the C-g -- and sometimes the
first C-g will update the display partway, and the next will update it
more.

   Burying or killing the *VC-log* buffer makes the problem go away.
Same with deleting the initial SPC character, which appears to be
necessary.

   I have had no luck tracking this down any further.  Setting
debug-on-quit not only does not enter the debugger, it sometimes seems
to cause emacs to hang indefinitely.  I assume the next step would be to
start emacs under gdb, but I am not familiar enough with redisplay (or
gdb for that matter) to know what to look for.  Any help would be
appreciated.

                                        -- Bob Rogers
                                           http://www.rgrjr.com/