Regarding the orginal topic, the initial wrong CAM message is a known bug. (But the resolution/source of it is still unknown).
For shorting the pin to ground to work you need something that will pull the pin back up to +3.3V or there won’t ever be a second transition on the line. Still, you normally would see enough noise from a floating signal to prove that it was or wasn’t transitioning. If you have one on hand I’d highly recommend clamping a logic analyzer on the pin, or using a LED inline with the shorting mechnaism to prove that the signal is making it to the pixhawk correctly.
I assume from your comments that you are trying to take a photo before looking for the CAM event? (We only configure feedback after the first trigger, and we only search for a single feedback event to tie to the trigger. I’m fairly sure this isn’t the problem you are actually having however.
Do you have any other device trying to use the pin? (RC_FUNCTION (or SERVO_FUNCTION’s depending upon firmware) any other RELAY’s/parachutes/etc using the same pin?
What FW image is this?