Hi
Glad to hear it's OK. I also mostly use 2.41 which, of course, only has 1 video track and an overlay track, as I find it renders and previews editing changes a lot faster than the latest version. Still, I'm not sure what your "flickering" effect might have been. 
If it comes back, post in with a bit more detail, someone will answer or give advice.That goes for any other questions. 
Nat