This has happened on almost every map I've played too, btw. Though I think its when I move my mouse around and start firing the skullthrottle, though, I can never seem to replicate it when I WANT it to happen. It's weird.
This is from awhile ago, and yes, I had been keeping up to date with the DRD gzdoom dev builds. Not really sure why this is happening really, as I'm not sure if its a problem with the mod or if its an engine issue. It's not a massive issue, it just means I need to save often.
Spoiler:Edit: Oh, and yeah it did happen again, though I haven't updated the dev build. Just an FYI. Gonna go get the newest and see if it happens, but I wanted to post this here first before I forgot.