Okay, I'm just following up with my solution. It's pretty obvious, and I should have caught it much sooner, and I'm kind of embarrassed to explain what happened, but for the good of the Game-Studio community, here goes:

I forgot to assign my variables a 0 value when I declared them.

I (almost) always assign a value when I declare variable. I don't know why I did not in this case, but that's why it took me so long to figure it out.

Happy programming!