I think I noticed this before on a larger scale and so i decided to test it. I raised the level of a tattoo along with spending xp and raised my PR. Then I unequipped my tat, and reequipped it. The bug is that the PR is now different, and when I mean different I mean it's now lower, not higher, then what it was before. Here are the numbers:
Original PR: 44,176
w/ tat off: 30,967
w/ tat on again: 44,147
I tested this again on my larger char but I got a 42 PR increase instead, but this could be accounted by a lag in PR update from the tat's levels. A better test would unequip and reequip that tattoo just after a PR update.
I think this may be from the recent fix that updates PR with tattoo advancement. Either calculations are off a bit or there is round-off error or something. In either case I shouldn't become weaker after applying the same armor to myself that I was just wearing. For people who don't unequip for a long time this may turn out to be a sizable increase in PR that should be lower.