Our CSS code needs to support some missing attributes like underline-position, underline-thickness etc. There is already a map in SVGFontFaceElement.cpp mapping these SVG attributes to CSS properties - but most are commented out. Should be easy to implement - but time consuming.
It's difficult to confirm this bug without a test case. We don't believe there is an ongoing issue here. If you do feel there is a problem, please REOPEN this bug and include a test case illustrating the issue.