I ran into this issue as well recently. I can't remember exactly what I was working on, but I did like Colludium did and just set the array.at to a variable and used the variable to compare.
I tried recreating it in a blank capx and I couldn't get it to happen so I assumed it was something else in my project. One thing was, I remember it being an older project that was started in a much earlier version of Construct 2.