Flash Operation - 10D

I'm confused... Please help me figure out what I'm doing.

When using the built-in flash (haven't tried the external yet - haven't needed to), in the P mode, I cannot get the aperture / shutter settings to change with the upper control dial like I can when the flash isn't up. Also, when I shift to Aperture priority mode, using flash, I end up with a really slow shutter speed, but when using the P mode, if it's at the same aperture, I end up with a much faster shutter.

Is there some sort of flash exposure setting that I'm not using properly? The only thing I can think of is that if I'm in P mode, somehow it gives a more powerful flash, but in manual or aperture modes, I get less of a flash. The exposure of either looks to be all right, outside of being blurry since I was handholding and ended up with something like a six second exposure when I switched to Aperture. Right after that, switched to P, and ended up with the aperture setting the same (wide open), and a 1/60 shutter speed. Same aperture, 360 times faster shutter, same exposure. What gives???

In the P mode, the upper control dial is used to shift the programming so that you get a different combination of shutter speed and aperture with the EV remaining the same. However, when you pop up the flash and you are in a not so well lit room, the shutter speed will automatically be set for the slowest shutter speed you can get in P mode which is 1/60. You won't be able to shift the sutter speed any lower because you're already at the lower limit for flash use. And you won't be able to shift it any higher because that would require a faster aperture and you're probably already at the limit of the lens as well.

When you are in Av mode, the camera sets the shutter speed that will allow you to get a properly exposed image for the aperture you have selected using ambient (or background) lighting. In Av mode, it doesn't matter whether the flash is being used or not, the shutter speed will always be based on the ambient light and not the flash.

The 10D is behaving as it should be and there's nothing that you are doing improperly. You just need to understand when you would want to use P mode and when you would want to use Av mode.

In manual mode you can get as much or little flash as you like, so it's hard to compare it to something else without knowing the situation and settings.