I had several bank upgrades, to around 100 slots total.
Upon relogging just now, I am back down to 60. I didn't notice at first until I noticed it was giving me "bank full" messages when I tried to deposit some things I had just taken out.
At the same time as this happened, I got an automated mail with another copy of the explorer's pack and beta monkey. Perhaps somehow my account-wide entitlements got reset?
I filed a support ticket 140407-081279 on this, but this makes inventory management just about impossible for me right now.