On the site we are still running 3.0.7pl1
At home in my test environment I have already updated to 3.0.9 (current version), will do the site update this week.
I'll look closer if I can find something I forgot here. I've been using this too long already, so I may have forgotten some change I made in the early stages of phpbb3
If I can't find anything then I'll pass it over to you because then I am sure the cause is on your side.
Give me a couple of days, pls.