I don't know how you feel about it, but I personally have wondered if it wouldn't be wise to think about a new site icon (favicon.ico). Maybe this old and faded vBulletin icon would also get a little younger and brighter.
This is an idea, coming from my old head, what do you think?
Most likely is it related to data conversion. It may be that there ia more than one empty space after word "Post thread" in language file (HTML5 allows only one empty space) or there is not correct encording - it must be utf-8 or in html5 <meta charset="utf-8">
But most likely it is more than one empty space as I said at first.
I think so, because if I look the page html source code, than there is correctly ...
I would recommend to look if there is something like lang.xml or any other language file, it may be there or look skin files, there may be something.
I can't do it, because .php files are available only from server side, not on client side.
And if You don't find, don't worry. I think, it don't bother anyone who hasn't been involved in creating websites themselves.
Sorry, I simply have such a bad trait, I can just see when somewhere in code is something wrong.