Hi all, realise this is an old thread, but hopefully this info will help someone else in future!
Same problem just happened to me - like one of the previous posters, I found out I’d enabled punch in and punch out without realising
It turns out that by default “activate punch in” and “activate punch out” are mapped to the keyboard shortcuts I and O. I must have pressed these by accident (this kind of thing happens quite often for me when I’m writing some text, e.g. editing a track name, but I’ve forgotten to double click on the text field and I end up accidentally pressing a bunch of random keyboard shortcuts!).
Since I don’t really use the punch features that often, I decided to remove the keyboard shortcuts so I don’t accidentally activate them again.
To do this, go to Edit > Key Commands, and look under Transport where you’ll find Activate Punch In and A.P. Out… click on each of them, and under the little “keys” box you’ll see a small trashcan icon - clicking on this will remove the keyboard shortcut.