I just updated the first mail with version V7b, that patches the problem in the V7 version.
For V7 I merged in some updates from the original xournal version, but these interferred with the code that tries to prevent scribbles and full-screen updates at the same time (which should limit hang-ups), resulting in 'fast-scribbles' being disabled always. This is now patched in the V7b version.
I was a little too fast in sending an update to the forum.