Gangplank shop bug..

Well, when i was playing gangplank today 7/23/2015 i found a bug for gp well for the shop... When i got 500 SS i went to buy the upgrade for his ult but i couldn't buy it when i had 509 SS (under recommended) However when i went to all items i could buy either one upgrade out of the 3....So i was confused why i couldn't buy the upgrades under the recommended items...