Don't know about downgrading to previus version either

But you should post the versions you have installed, I meen mypaint and mypaint-data. I'm pretty sure thats where the problem is for you.

Write in xterm:
apt-cache policy mypaint 'enter'

apt-cache policy mypaint-data 'enter'

Your problem sounds alot like mine i had and that got fixed with an update of mypaint-data only

Mine looks like this:
~ $ apt-cache policy mypaint
mypaint:
Installed: 0.8.2-1maemo10
Candidate: 0.8.2-1maemo10
Version table:
*** 0.8.2-1maemo10 0
100 /var/lib/dpkg/status
~ $ apt-cache policy mypaint-data
mypaint-data:
Installed: 0.8.2-1maemo10
Candidate: 0.8.2-1maemo10
Version table:
*** 0.8.2-1maemo10 0
100 /var/lib/dpkg/status
If yo want to compare

@Tone i joined the bandwagon and oc'ed my N900 and must addmit that it's a plessure to use in mypaint. I have mine set at 1000, maybe i'll try to raise it some time. I only use the high Hz when i use mypaint