Email links causing strange redirect that happens only once untill browser cache cleared.

[System]

After some advice on this issue.
I get a lot of (legitimate and wanted) email notifications to a forum I am a member of. The emails include a link to the latest posts.

Today on two different PC's (one Vista IE9 and one W7 IE10) I find I get redirected to a file sharing site when clicking a forum link in one of the notification emails. Another window also prompts to download an HD codec (that site looks suspiciously like
Adobe but isn't). If I click the same link again it works as expected taking me to the correct forum posting.

If I clear IE history the same redirect happens again... just the once.

What is even more strange is that the Vista PC is not deleting the cookies and login info for the legitimate site that sent the email when I run a full browser cleanup. I can still enter the site as logged in. I also can not open an "attachments" window
on that forum on the Vista PC since this happened.

Does this sound like any kind of malware etc. I run MSE on both and both come back as clean.

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