RoundedCornersExtender Border Issue

I'm trying to implement the RoundedCornersExtender within an installation of DotNetNuke 4.4.1. Something is causing the right corners to be cut off two pixels too early in IE when using the Extenders border attribute, making the border look incomplete. The border renders correctly in Firefox. I've futzed with all the border, margin and padding settings I can, but the corners are still being either rendered incorrectly, or the divs containing the rounded bits are shifted right. It feels like an off-by-one error, but I wouldn't have the faintest idea where to look.

Any ideas?

Hi have the same problem just using a standard aspx file. I've just found that this only happens when using certain DOCTYPE. In my case i'm using:

<!DOCTYPEHTMLPUBLIC"-//W3C//DTD HTML 4.0 Transitional//EN">

I cannot change to XTML 1.1 because i need certain components that just work using the current DOCTYPE. In FF everything is ok in both DOCTYPE scenarios.