I just installed Krita on the Windows partition of my iMac. When I tried to use it, two things happened; first, it didn't recognize pressure sensitivity (which works fine in Photoshop, so I know it's not the Wacom driver) and second, when I lift my stylus from the Cintiq it stops recognizing the stylus. That is, if I touch the stylus to the screen again, the brush stays where it is. I have to click on another part of the interface, after which the program responds to the stylus again.

Any ideas?

I'm having this same exact problem with my cintiq 13HD. The pressure sensitivity works fine in Painttool Sai though.
I run windows 7 64bit and have tried uninstalling and reinstalling my tablet drivers and krita and nothing seems to help.