I often read Geekzone on my computer at home and also on my computer at work. However I notice that when I've been reading Geekzone at home for a few days and then read it at work I get lots of messages that I've already read. Eg I read Geekzone at home yesterday (6th Oct) and when finished I clicked on the "Reset read flags" link. At work today (7th Oct) when I clicked on the "First reply since reset" icon next to a thread title I get taken to messages that are older than 6th Oct (eg I get messages from 2nd Oct).

Is this because the forum is using cookies to track when I last read the forum and the cookies on my PCs are out of sync? I can't think of anything else that might cause this.