this has already been reported but i would like to provide more information as it might not have been seen as an actual bug
if you buy a voucher tag going into the boss, you'll have two vouchers you can buy at the shop after the boss. however, if you only buy one of the vouchers before leaving the shop, the shop will be completely empty of vouchers afterwards until the ante after that. i have tested buying both the left and the right voucher, and this still occurs regardless. this doesn't make sense as unbought vouchers are supposed to stay until the next ante.
a fix could involve adding an indicator for which voucher (or vouchers for multiple voucher tags) are temporary for that shop only, and keeping the other non-temporary voucher to be purchasable in the next shops
