Gold Bug

I was playing last night after the server restart and was sitting in base waiting for 7 gold to get a pink ward. I was at 74 gold, the enemy Twisted Fate ult'd as I bought a pink ward but the gold did not get spent after getting 1 and I was able to purchase 2 pink wards for 75 gold. I'm just wondering what type of interaction it was, and if it were a different component like Zeal, that would be a terrible bug.