Biscuit Delivery Causing Item Undo to Grey Out

I was playing Rakan on Summoner's Rift and upgraded my normal boots to Mercury's Treads. Looking at enemy comp I decided to undo that and get Ninja Tabi instead. As I was moving my mouse down to click "Undo" I received a Biscuit Delivery and the Undo button went Grey. That is, it became impossible to undo the Mercury's Treads purchase.

Other info:

This was coming from a Respawn, so I was not moving.

Time between purchase and my choice to go back was less than 5 seconds.

I assume this has something to do with the biscuit delivery being treated as a separate store visit? IE the store session is closed, a non-visible inventory space generates a biscuit, the store now shows that there has been another store session since the boots were purchased.

Rare and not the end of the world, but figured you would want to know.

-Zagdag