Relic Shield Buff Lost After Upgrade

Played a match as Thresh tonight where I upgraded Relic Shield to Targon's Brace, then clicked "Undo" to purchase a Sightstone instead. When I got back to lane I noticed the buff was completely gone; not as in I had no charges, I had no passive effect on my bar. It did eventually return within a couple minutes, no more than 180 seconds I would guess, and I had no further issues with it.

I should note that I did try to proc it while the passive was not noted and had no results ( no gold share ). Once the buff returned procs were standard.

Steps to Reproduce:

1. Purchase Relic Shield, proceed to use as intended.

2. Return to shop and upgrade Relic Shield into Targon's Brace.

3. Click "Undo" button to revert Brace back into Shield.

4. Purchase Sightstone.

I haven't made an attempt to recreate this personally so I've only seen this once.