Not true, I know that at least in old versions of Netscape you can set font attributes to affect buttons, such as color and boldness. I don't know if current versions still do that.
All that aside, it's relatively trivial to run your post through an HTML validator before sending. For big posts I usually cut and past into a word processor for a spellcheck (because my is horrible). Perhaps the wise and mysterious vroom could put in that added functionality, but I wouldn't really call it a bug.
...you might be eaten by a grue...