Nice! I started to use this for learning the lowest level of code (even made a tiny but pitiful compiler, perhaps I'll add additional functionality like ADD and SUB), but it seems that occasionally the code will never loop or freeze up if I try to create an infinite loop. I know it's been about 2 years, but you still asked to mention about bugs.
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Hello! The reason the program seizes up if you try to make an infinite loop is that it tries to run through the entire code on a single frame. It runs the code every frame so technically everything in 4BOD is an infinite loop and it's more difficult to make something run only once. I know this isn't exactly the best way to do this but hindsight's 20/20 and like you said, it's been 2 years.
If this doesn't help and you're sure you've found an issue with the program itself then I'm afraid I can't really help since I've managed to lose the source code for this thing. The only thing I can do to help in that case is recommend you to use the Windows build instead of the online version since it's more stable.
Hope this explains your problem.