setup: a630 +16gb card without multipartition.
in the morning I did about 80 photos without chdk - they were placed in new folder (as expected).
then alter some tome(switch off/on) i decided to run intervalometer and launched chdk.
but I forget about 60 seconds override i did day before so I in a hurry tryed to stop script by pressing "shoot".
of course it would not stop for next 2 minutes so i pressed power button.
result: I lost all previous photos done this day which were in newly created folder.
Of course i could try to use some software to undelete/restore images from sd card but I realised erasure fact too late (alot of sd card overwrites were done after that power off) and I did not have replacement sd card by hand anyway.
I did not try to reproduce this behaviour yet - I did not backup my sd cards after vacation.
I think it is not related to chdk.
Will try to reproduce this problem without chdk with native 15 seconds override.
edit: changed subject to clarify that i switched camera manually