|I know, the picture is flipped...|
Then, I put it up on the bench for a different issue altogether (added a strap button; no big whoop). On the bench in the light, I noticed something looked wrong about the "B" and high "E" strings. After putting the calipers to it, I figured out I had swapped those two in the last (first) restring... a month ago.
I went a month with this issue and never once thought that I had done something wrong. Now it all makes sense, but I was really getting unhappy with playing the guitar. Boy am I embarrassed!
It just goes to show you that no matter how much experience we have, we still make really obvious mistakes and it might take a completely different perspective to understand what went wrong.