@horace-miner When you exhange an item you will get the generic spendable ACE voucher, and you will retain credit towards the STR?AGI/whatever vouchers acquired gates. These values don't go down, think of them more like XP towards unlocking the pack, then once you hit the gate you can spend the generic spendable ACE vouchers.
To test this, check the ACE section of the store for STR vouchers, grab an STR multi-voucher from the bank, then pop to the exchange and redeem it. Now when you check back on the store page your generic ACE voucher balance will increase, as well as your "STR Vouchers acquired" counter.
I know this isn't the most intuitive system in the world and I've seen quite a few reports on it, but any time I've looked into it things appear to be working correctly. If you have any screenshots or clips indicating otherwise please let us know.