So Eli at Piko Interactive was testing Anguna, and kept running into a problem where the main boss would disappear halfway through the fight. Not that the dragon would really go away, but the sprite would disappear, but the collisions/bullets/etc would still continue.
Try as I would, I just couldn't reproduce it. He said it happened 100% of the time. But I couldn't see it happen. He sent me a save state and said that it should happen just right after loading from the save, but I still couldn't reproduce it. Finally, though, I just entered the cheat code to get tons of health, put the phone (emulator) down, and when I picked it up, he was gone.
So after quite a few more experiments, I somewhat sorted it out: It happened at 3ish minutes into the boss fight, every time, like clockwork. But the way I played, I never lasted 3 minutes in that fight. I always played it more aggressively, and was either dead or victorious in a minute or two. I never saw the bug, because I played the game differently (this is a good lesson to us programmers: sometimes people use our software differently, and expose completely different behavior than what we usually see! As a side note, the other day I had a problem at work, where a user said a field input NEVER worked. And it always worked for me in testing. Turned out, she always clicked the submit button, where I always pressed enter. The enter key worked. The submit button didn't. oops)
Anyway, once I figured out how to reproduce it, it didn't take long to find the problem. I opened up the code for the boss fight, and saw that the animation for the face (which only had one frame) was set up to display for 9999 game frames...then was supposed to start over (back to the one frame again!). 9999 game frames was about 3 minutes. Aha! Turns out my code to start the animation over wasn't working right for these one-frame animations.
Which meant that there might be other issues with single-frame sprites. I dug around and looked -- most of them were set to some absurdly high number of game frames before they "repeated". Turns out, if you put the game down for about 30 minutes without moving, a bunch of things (doors, items, locks, etc) timed out and disappeared. I guess nobody's ever tried doing that, that bug has been there from the beginning, but nobody has ever reported it!
It only took one line of code to fix it, and make the single-frame animations loop properly. Weird to find and fix a bug that serious and that old, with 1 simple line of code.
Assuming no other issues appear, manufacturing for the cartridges should start soon, according to Eli!