It's not a skin problem. It's in the postbit code itself. vBulletin works by grabbing all buttons, text etc. from a language database table. The postbit code grabs this text from the database and displays it. This means the language table is corrupt and indexing the wrong row. That causes it to, at times display the wrong code. I've repaired the database now, so it might be fixed. Let me know if it happens again.