It's always interesting to hear in what contexts users seem to be using Diarium.... 🙂
I have made several adjustments to the copy/paste logic in recent updates, the last one being this one.
At the moment (with the dev version of the app) I don't see any issues when copy-pasting text into the app - no flipped lines or lost formatting.
If the problem continues to happen with v3.1.11 (already available in the store), please let me know (and ideally provide a screen capture recording to me via mail) - thanks!