Confusing pocket values for automatic tool change remap

I'm slowly getting the ATC on my router working, but I'm running into something very confusing. I'm using Axis, and I'm working on my NGC for the M6 remap.

I have 5 tools, and my tool table has the same tool and pocket number. I read that the pocket number is ignored for non-random toolchangers (mine is non-random; it's a rack of forks at one end of the table).

When I go to load tool 1, my code gets called with selected_pocket 1. When I go to load tool 5, my code is called with selected_pocket 4, not 5.

I've attached my NGC file.

At first I thought maybe pocket numbers were 0-based, but that's not the case for tool 1. I'm very confused. Any ideas? Thanks.