I found a new bug.
Pro-tip: Do not use the poison whetstone on the vampiric axe because you won't like the result.
I am sure it is a bug because this weird behavior occurs with the mirror shield too.
Basically, the issue with the mirror shield is simple: whenever the player adds a spike effect to it at the forge or with a spiked scale, it overwrites the shield's spike removal effect.
edit: Added a strikethrough to one statement. (The spiked scale acts independently from the shield, I believe)