Hey again, sorry for the lack of details. I was a bit upset so I posted and ran away for work.
So. I made a little video to show what is happening: https://drive.google.com/open?id=1TQPYs4US5iX7bYNQtgJEm2K-nSPZxXt9 (the software is in french because, well, I'm french)
The bug points on the middle of the timeline and not on the red line. "When I zoom" means: "on the timeline." The problem seems to happen when I click on a split. And my mouse works fine.