[Gameplay] Sightstone Charges Not Refilling?

I don't know what exactly did it, but in my last game I played support Nami, and at some point my sightstone stopped refilling charges when going back to the store. I think this persisted through 3 or 4 backs/deaths before I sold and rebought it, at which point I was given the proper 3 charges. I asked the Bard on the other team if they had the same problem, and no dice. If it happens again I'll update, but this was pretty annoying!

Edit: Was watching imaqtpie's stream, the same thing happens to his Gragas's jungle item charges here.