If I'm playing a quick pattern like this and holding down some bass note, depending on where the pattern starts, the middle two notes will become "synchronized" and play/get recorded at the same time. In my example, the top 4 notes work fine, but shifting down by one note causes the bug. I also switched between holding the bass not and not for demonstration. I assure you my fingers aren't doing anything different, I messed around with this for a while.