Incorrect read/unread status

I'm continually irritated to find messages that I have never read, being marked as read.

I even tried to ask for help on the vBulletin site, but since I'm only a user and not the software license holder, they respectfully declined to talk to me.

I fear my problem is actually a "feature" and not a "bug" (sarcasm implied), but it annoys me, so I figure it annoys other people as well.

What I want is simple:
Every thread I have not read should be marked as Unread, regardless of how old or stale the thread is, or how long since my last login.

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I hope someone can find a solution to this problem.

I wonder if it would help if I manually marked each forum as Read once. Would that reset all the flags?

Also, I'll admit that I use two different computers, but I don't think thats the reason for the problem. Is my read history stored on the Forum server (globally available) or as a cookie on my PC (locally available)? I hope it's global.

I'd be willing to help someone test different ideas, i.e. volunteer my time, to help fix this this problem.

Thanks.