Mayan Temple Add Detail Challenge but having Inset confusion

Hi. I posted this somewhere but don’t think it was in the right place. Sorry about the double post but I’m getting very frustrated. Sigh

I’m actually working on the Mayan temple and
supposed to experiment with making some temple details. Well I was going
to start with an inset in the top middle face. I selected and hit I the
set Thickness to 1 so all the vertices would meet in the middle. That’s
NOT what happened. I went back and checked normals and they were ok. I
made a new cube and it worked ok. I thought that maybe for some reason a
rectangle instead of a square made a difference on my new cube and it
didn’t seem to. I have no idea what’s going on. Here’s a picture of the
ace I was working with and what it looks like when I did “I”, then left
click, then change the Thickness to 1. Any help will be appreciated.

Another note. I tried making a triangular face and doing “I”. Really weird results.