Sorry for the delay in answering. ubuntu-geek is out this week on personal business, and I just didn't see the revived thread.
I also apologize that we never got around to answering this question. I am guessing this is being caused by page caching on our local server.
If I look at an old thread that I contributed to, and then change my signature, then reload the thread, it shows my old signature for a period of time, and then eventually it changes to the new one.
If I change my signature and then look at an old thread that I contributed to, which I know has not been viewed in a very long time, my new signature appears immediately.
So, I'm going to say it is a feature, resulting from the page caching that is turned on to help reduce database queries and server loads.
Can you confirm that your signature exists correctly on old threads after a long time?
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