Nothing in particular, just playing/editing/whatever. With or without crashing. The only thing I
think triggers the bug is using lots of big/heavy/bloated programs/games before starting DROD. Yesterday I used many programs and a game that consumes many resources, about 10 hours without rebooting, all this before starting DROD. Could it be something about low system resources? But after the bug, I started MS Office, BitTorrent, and Diablo II; all went smoothly so I'm out of clues
To anyone hunting this bug: make a backup of DROD's dat files everytime you are about to start the game. If the bug manifests, see if you can trigger it again with the backup after a reboot. I'm trying to do this, but always forget about it