I just started having the same issue that was posted in this thread http://www.kdenlive.org/forum/mouse-cursor-freezing-kdenlive-76

was running 8.1 SVN under Natty ( ubuntu classic interface ) happed once the went away after a reboot. Now it's back and won't go away.

This just stared happing a few days ago, up until then it was working fine.

when kdenlive starts the mouse freezes. As soon as it stops the mouse is back. I have tried the --nograb and just about every other command line option I though might help.

Did a complete removal of kdenlive and melt and then installed 8.0 with the same results.

I am willing to help debug to find the issue, I just need some ideas on what to try/do.

Edit - after struggling with this for about a week I found the issue just after posting. My jog shuttle had changed device names/numbers and the Jog Shuttle device had changed to the mouse in the KDENLIVE config. After changing it back things are working fine. little bit of a pain to get to the proper config menu w/o a mouse but all is good now. So now back to 8.1 SVN until 8.2 is released.