Problem with user activation links
Just to add; we are apparently seeing this issue too. Or to be more clear: we haven't seen it ourselves, but our client keeps getting reports from their customers that Activation links are not working - giving "error messages" when clicked. We've then had the trouble mail forwarded to us, we've clicked the link, and it's been fine.

Looks like there is some mail client out there mangling the activation links. Which is bad. And we don't know of a solution.

The codes are not expired.