Webber's Wonders - Perform Bonus cannot be applied to clothing

[Poolson]

When attempting to purchase a perform modifier bonus on clothing obtained at Webber's Wonders, I was given the prompt of purchasing it for 400 gp, as normal.

However, when the option is selected, the NPC says that the process is completed, but will neither take the gp or add the bonus, while still counting towards the limit of skill bonuses & save bonus (2 skill bonuses, 1 save bonus).

This was on Ghaela Stellrum.

[Poolson]

Trying this on normal clothing, the result is the same.