Oil cap wtf?

[zen.C10]

My truck is new'ish to me, and I thought I worked through most of quirks but I came across a new one over the weekend. I went to top off my oil and realized the oil cap won't come off - it just spins in place.

I know I can add oil through the PCV, but what's the deal with the cap? Shouldn't I be able to remove it? Am I missing something or is this a sign of a bigger issue?

I'll probably take the valve cover off to see what's holding the cap in place, but I figured I'd ask you all before I go that route.