I ran the test with remote enabled and disabled. With the remote disabled my laptop was recognizing the camera. with the remote enabled it was not. That seems to make sense but no indication on voltage changes.
I'm travelling right now so won't have access to my dev machine until Friday. However, the fact that your camera behaves differently when connected to your laptop depending on the remote enable/disabled status suggests that
#define USB_MASK 0x40
#define USB_IDX 1
in kbd.c for the ixus750_sd550 are probably correct.
However, there appear to be some probably unrelated funky hard coded key masks in my_kbd_read_keys() for that camera. Will take some digging.