G1 changing image size by itself

I just came back from a two-week vacation where I used my G1 + 1Gig Microdrive daily. Now the weird thing is that at some point it switched from the highest resolution (which I had set) to 640x480. After that, some pictures I took were stored at that resolution, some at the highest resolution. Has anyone seen anything similar? What could make the camera to behave like that?

I bought my camera last June, so I guess it doesn't have latest firmware updates.

Before I switched to RAW format, once I noticed, that different setting on the dial knob can store different resolution. I do not recall what position had what, but you can try to set the image resolution in one of your favorite position (auto, P, Av, Tv, M and the other 4 preconfigured ones) and you will see, that not all will keep the same resolution. For e.g. one position was set to 2000x1500, and another was left at 1024x768.
Geza

Thanks, that explains it. I did some tests w/ my camera and it appears that it stores two sets of preferences - one for all "auto" modes and the other for all "manual" modes. I still wonder though, how it switched to 640x480 in the first place?