Thank you for writing and for the provided details.
The Html-like feature has a known issue related to the incorrect painting, because some fonts do not report correctly their text metrics. For example, Segoe UI and Tahoma with font size 8.5 do not render correctly - they report incorrectly some text metrics and changing the font to Segoe UI with size 9 (or Verdana 8.25, which looks pretty good) fixes the incorrect rendering.
Please let me know if this help for your case
the Telerik team