When attempting to apply +perform bonuses to custom tailored clothing for 400 gold, the vendor will neither take your gold or apply the bonus, but will count towards the total bonuses towards what you can apply to your clothing.
This was noticed with the NPC Chief Tailor Selarus the VI, in the Peerage Ward shop "Treasures of Magus Naoli Thrazulebh".
should be fixed
Just checking in to say that I just tried it and it's still a persistent bug.