Ive found that after clicking in any button of mission planner you can “click it” again by pressing the Enter key instead of using the mouse. The only way to not have this effect is to click on another button or tab. This is quite concerning for the Arm/Disarm button, given that after arming you may accidentally disarm it. Or even worst, you could accidentally arm it after disarmed and injure someone.
I’m pretty sure this is a MP codeing overlook, so I don’t know how could it be fixed except with an update… But I thought you should be aware of it and take precautions to avoid it.