Sounds to me like you need to add border="0" to the Rich Text version html.
I'm assuming your Rich Text version is just the standard:
HTML Code:
<img src="/images/prefix.jpg">
Change it to this:
HTML Code:
<img src="/images/prefix.jpg" border="0">
When you link an image, there is a standard border associated with that image link for some reason. You have to specify that there should be no border if you don't want one.
@vbenhancer... nice hack. I thought this was what the prefixes were supposed to do already but when I started using them last week I was surprised they didn't. This should be vbulletin by default. In fact, I don't really see much of a point in having them if they DON'T do this. Great job!