Not sure if this was mentioned before but I discovered it by accident cause I don't read instruction booklets
The G10 (probably other models as well) can't shoot a faster shutter speed than 1/500 when using the strobe because that's its max sync capability with the strobe.
I shoot in the M mode and was using 1/1000 shutter speed. Little did I know the camera was automatically defaulting to 1/500 when the strobe is on. I discovered it when checking my EXIF data and it showed 1/500. Guess if I read the camera booklet I would have seen it sooner