Your experience with Bluetooth HID on the Bangle?

Does the 'key stuck on' problem happen more often than just the missed key?

I don't think so - I would say the repeated key is just more noticeable than an initial keypress missed, but I could be wrong.

What exactly happens when an HID report is sent? Is there some sort of handshake or request/response with the receiver to make sure the packet has been received? Or is it just fired out in the hope the paired device receives it? From your comment I seem to understand there is a difference between the callback being triggered and the report actually being sent out / received?