Left mouse button stops working?

[Graham Williams <Graham.Williams@cmis.csiro.au>]

I've a strange situation.  The left mouse button ability to click has
suddenly disappeared?

I recently upgrade some packages (I'm essentially running the unstable
Debian distribution) including xlib to 4.0.1 (but not all the way with
xfree 4.0.1 yet). I run Helix Gnome and sawfish. Sometime in the past
day one login account's left mouse button stopped having its "click"
recognised within windows (The sawfish window decoration gets it just
fine---seems like it is somehow turned off inside of windows - for
example I can not click buttons or lists within the GUI, nor click on
icons in the Gnome panel to start them up - I've tried changing GTK+
themes in case this had some bearing on the problem)! The other two
mouse buttons work just fine and on other user accounts ON THE SAME
MACHINE everything is just fine!

I've hunted around for likely causes but now need hints on where to
look for the likely culprit?

Oddly enough, Shift-LeftMouseButton also works just fine!!!!!! (so I
can at least still work with those applications that thankfully seem
to equate Shift-LMB with LMB - not all of them do but GNOME seems to
:-).

Thanks,
Graham