Confirmed - it went weird after a private tab was opened with me by another member. It already displayed some bizarre behavior such as private tabs not closing, and not being visible to the member that opened them. As well, when trying to close the errant tab, it would instead close tabs at the other end of the chat window.

I'll attempt a reset at the various levels until something works. Now, where's that manual?

[Edit: nope, no luck there  ]