Donating and buying back spent wands/staffs

[robinjohnson]

Giving wands and staves with zero or few charges to the magic shop seems to top them up when they're in the store's inventory, but only sometimes – I can't figure out what circumstances it works under. It might only be happening for wands that the shop has a chance of stocking. Once I've got enough money, I do it with my slow monsters every time I'm back in town. Is this intentional, or am I exploiting a bug?

[Nick]

It might only be happening for wands that the shop has a chance of stocking.

This is it, not a bug.

[m0stlym0nk]

I wonder if there's some way to hint at that? Perhaps an alternate bit of "talk" text from the shopkeeper on player drop/sell of the item, along the lines of "I don't normally stock those, but ..." etc.