Dupes Stuck in Ceiling

I was digging out an area with sand, and ended up with 3 of my dupes caught in the ceiling, with them suffocating until I was able to dig them out.

I'm not exactly sure how this happened. I suspect a dupe got up on a tile beneath two sand tiles as the first sand tile was in the process of falling, so then when the sand finishes falling it pushes the dupe up and into the tile above it. I then had other dupes dig out the sand, and realized what was happening and took a screenshot after that.