depart messages aren't being sent as expected

[pvh]

Not quite what the cause is, but I suspect something with over-counting the s on the presence heartbeat.

To reproduce, put a breakpoint at the depart callback in the heartbeats hook and then try navigating away from the board you're looking at.

I discovered this while testing selection clearing when another user navigates away. I suspect it's reproducible pretty easily, but LMK if you have trouble.