[Gameplay] Frostfang Tribute only granting 5 gold, tooltip says 10 gold

I was playing a Co-op vs AI game as Nami. I got Spellthief's Edge, and later upgraded it to Frostfang on my first return to shop. Everytime I triggered a tribute, it only said +5 gold above the target. I checked that the total tribute gold in the tooltip was also only increasing by 5 gold. Once I upgraded to Frost Queen's Claim, the tributes began being 10 gold. I was not able to check if each tribute was actually increasing my total gold by 10 or by 5.

According to the tooltips, Spellthief's Edge should grant 5 gold per tribute, and the later upgrades should grant 10 gold per tribute. This may be a bug because this item was recently removed from the game for a bug just a few weeks ago. I tried another game to see if it would happen again, but the Frostfang tributes were 10 gold that time. I'm not sure how to reproduce the bug.