Problem with undoing purchases whilst using the 'Biscuit Delivery' rune.

So I was playing Nami in a ranked today and I took the Biscuit Delivery rune. I went B at one point and bought Frostfang but changed my mind and tried to undo the purchase and instead buy a Sightstone . However, in the time between me purchasing Frostfang and my attempt to undo the purchase, I received a biscuit due to my rune. This meant I was unable to undo my initial purchase, which seems like a pretty dumb issue to me. Surely I should be able to undo my purchase whilst the biscuit has no affect on me doing so? Please fix this xxx [zombie-brand-facepalm]