counterfeit penny is a passive item?

[Lord Tony]

so I noticed counterfeit penny is in my passive item list and when I pick up a penny I collect 2 instead of 1

however it is not in my trinket slot and I don't know how I'm gaining its effect

[M7SN_X]

There are a couple of things that can cause this, either active items or a pill. But you most likely used a gulp pill, which puts your current trinket into the passive items tap so you have it permanently.

[Nazemec]

Gulp pill, Marbles, and Smelter can do that.
Maybe others, but these three are the first I can think of right away.