I'm no THF, but I just think of it as a DNC. Steps hang around 30 or so seconds, and are set to 30 seconds again each time they are triggered. TH could be similar. That would make people dying and staying back lose TH, while people who die and engage again within 30 seconds (or other magical time number) will see it stay.

I could also imagine stuff like Booty Shot confuse the system to lose TH numbers. Also maybe that is how some report TH12?