Ah... I see that now. It is very slight. I'd throw it in the bug tracker. I doubt it will get a very high priority though for now.
This is the problem:
On the Forum page:
HTML Code:
input, textarea, select, button {font-family:Tahoma,Calibri,Verdana,Geneva,sans-serif;}
On blogs:
HTML Code:
input, textarea, select, button {font-family:Calibri,Tahoma,Verdana,Geneva,sans-serif;}
Post that in your bug report so they can easily see what the problem is.
(If you want to change it - stylevar vbblog_input_font is the second one. Just change it to what is in the first one.)