I was hoping to find out abut the same thing. Is there any chance of someone writing a clear "instruction manual" or "step by step" type post for this (or a module that handled it would be great)? I am not to this point yet, but I can see it's coming and would like to be prepared.

I've noticed the exact same problem. It doesn't happen with the same install of newbb on my older site using XOOPS 2.0.16 but does happen in the new site I've been working on using XOOPS 2.0.18.1, so it seems to be something with XOOPS and not newbb that is messing it up. Very annoying and I would love to find out why it's happening so we can fix it.

I am having the exact same issue, but I have been including that line in my style the whole time. I have also tried all sorts of other changes to the code, but I am still getting the result. I use other themes (many of which I have even tried to cut and paste the code from) and they work fine, but mine won't work no matter what.

In fact I was coming here to post a question about this issue, when I saw this post. Hopefully somebody will have an answer... or at least a suggestion.