OK, so I fiddled with it some more and it looks as though there is a height limit of four lines on the signature. Problem is, that whatever is there to check the signature doesn't take in to account any tags (like the link tag [a href...]), it just applies the height limit before evaluating the tags, making the tag contents part of the limit, as if it all were visual text. It should be the other way around, I think.

So evaluate the tags first then apply the height limit.
While this seem to be the case with preview signatures, it is not the case in the forums.

Any chance you will put this on your todo list, Ken?

That be great, please let me know when or if you fixed it, thanks