Blind transfer not working on hangup bug

[mrabbitt@clarkecounty.gov]

On my T52S phones running 84.0.10, I've noticed a bug where if I hang up the handset at a specific time to complete a blind transfer, the phone instead behaves like it's in an attended transfer. This causes another major issue which I'll get to after explaining the first one.

Here are some relevant config changes present on my phones:
Semi-attended transfer is disabled
Time Out for Dial Now Rule is set to 1

Reproducing the bug:
1. Answer a call taking the handset off hook
2. Press "Transfer" button and enter extension you want to transfer to
3. Hang up the handset after the Dial Now Rule timeout but before the transfer-to extension starts ringing

What you would expect to happen here is to have the call blind transfer. Instead, what happens is the phone goes into some kind of invalid attended transfer state where if you hang up the Yealink phone, the extension you transferred to will continue to ring. Once that call gets picked up or goes to voicemail, you will hear the audio play on the Yealink phone even though it is on the home screen and no longer in a call.

If you do the transfer and hang up before the Dial Now Rule timeout finishes or after the transfer-to extension starts ringing, the call blind transfers correctly.