Here's what I did to make it happen again. (Circles represent pulses)
It's rather inconsistent, but you can see how this could happen in casual play (e.g., if you are trying to simply push the whole box up, and then suddenly it separates)
Viewing post in Full version in development! comments
Hi BerryGo. Thanks a lot for this info. I’ve only been able to reproduce this bug a few times myself, so this is helpful. I’m planning on releasing an update for this version of the game (hopefully with a fix for this issue) around when the Steam page for the full version is finished, and I’ll be referencing this :)