Red buff regen lost upon attacking structures

Title. This isn't mentioned in the tooltip at all, which states that it's only lost upon entering combat with a champion (e.g. not lost with minions & jungle monsters).

It's lost against all types of structures, including turrets, inhibitors & the nexus.

This is significant when splitpushing deep in, say, for after killing the enemy that backed to stop you then dying to another enemy who backed because you didn't regen while attacking their structures.