The next time this happens, could you send a copy of your file to omnioutliner@omnigroup.com please? It may have nothing to do with the configuration of the file since your solution is to copy it to a new file, but the more information we have the better.
Just installed Outliner 4.1.3 Pro on a new rMBP running Yosemite and can consistently reproduce this error by:
Create a new document
Add a couple of level 1 rows
In Styles select Level 1 rows
Change the font size or bold
Return to the document and attempt to add another row
I’ve reproduced this on all new documents so it doesn’t appear to me to be related to a specific file. I tried trashing preferences and this didn’t help me either. I’ve also had the app crash. I will contact support and attach the crash logs.
Ah, thanks for the steps! Looks like I can only repro it when using a retina screen, odd. But, good new is this appears to be fixed the next version we’re getting ready to release that fixes the last Yosemite issue we’re aware of.