It just started today here on an fully upgraded (I left this post also in Ubuntu+1) saucy i386 on my Sandybridge B75MA-P45. I was finally able to post screenshot after 3 times (on that machine in Ubuntu+1 subforums. Let me try this machine:
..ok.. I just tired it with a Maveric install on another machine and it's completely busted, Will not allow screenshot and does not give any notification.