"skull-icon not always visible when player is out" is a newly discovered bug from this thread. So far no details are known for how to reproduce it--what gamemode, for example?--but perhaps if it gets a thread, somebody will figure out some more details.

I tried this with hosting in 6.3 and joining with 6.6a and vice versa, and letting different clients win in different orders and using the /cycle, but sadly I could not replicate this.