I think this might actually be a glitch after all.
Look at this image:
<img src="http://img856.imageshack.us/img856/3733/n8ud.jpg" border="0" />
This is of 2 different screen shots of the same text. Note that one has a bleed over. The other, doesn't! The difference between the 2? I ever so slightly tweaked the spritefont object's size. That's all I did. All of the other settings are the same.
Wouldn't this suggest that there isn't a bleed? I have ample spacing, and used the spritefont generator, following its instructions to the letter (HA! Pun!).