Oh, I didn't try select to reset. Thanks!
About the cursor bug: I *think* the number of levels before it happens varies, but it's possible that just depends on what level I was playing last time I reset or how far I was from a "problem" level when I resumed play on any given day. It usually took a good while to happen but happened regularly enough that I got used to it, but I wouldn't be able to tell you how many levels it took. Somewhere on the order of 100-200 maybe?
I did mean power cycling fixes the problem when I said resetting. Unfortunately I don't remember whether returning to the level select fixes it, and I never tried returning to the menu. I ended up always resetting for a reason, but it's possible that reason was simply speed. Naturally, playing through over 200 levels just now (1-133, 4521-4661) to see if I could trigger the bug didn't achieve anything xP
It's weird that the glitch is preceded by laggy behavior in the cursor during normal gameplay. The cursor becomes laggy in the middle of playing a level, rather than right after it's first loaded. This symptom makes me doubt it's related to the way the levels are stored. I also don't remember the glitch happening even once during the early levels, so I wonder if perhaps it's connected to time spent playing a given level, or time spent playing in a given session.
I'm sorry that I don't have more specific information! I'll reply again when I have something to share.