That is one strange looking Expert workspace Timeline. Are you seeing the same type of thing in the Quick workspace Filmstrip space?
Let us start by deletion the Adobe Premiere Elements Prefs file. I believe in Mac it should be found
Users/Owner/Libraries/ Application Support/Adobe/Premiere Elements/13.0
If that does not help, then the usual questions
1. Is your video card/graphics card AMD Radeon HD 6750M driver version up to date according to the web site of the manufacturer of
2. Does the problem exist with or without the antivirus and firewall(s) disabled?
3. Are you working with pen and tablet device or mouse?
Let us start here and then decide what next.
I'm afraid this was not correct:
I am running on an iMac 2,5 Ghz i5 with the latest software updates installed
OS X Update 10.10.2 solved the flickering issues which only occurred in the expert workspace filmstrip.
Apologies and thank you,
Great news. You did a great job sorting through the details to gain the success.
Thanks for reporting the outcome on what was a very unusual Premiere Elements 13 Mac happening in
the Expert workspace. That report will be especially appreciated by others with a similar problem looking for solutions.