I can't solve your problem for you, but I can offer some insight.

If an ISBOXER mapped key is assigned a hotkey then ISBoxer will "intercept" the hotkey and only do what the mapped key is programmed to do. So in your case, I bet you'll find a mapped key that sends F8 whenever the space bar is pressed.

Try using the guide posted by Apps. It's the second one listed in my stickied guides thread.

Good luck