Glad you had fun, thanks for playing!
Save game should ameliorate the problem, you should be able to play again where you left off after loading save. Please check which version you're playing, as we added a fix that might prevent that bug in V0.007 If that's the version you played we're going to have to keep hunting for a way to reproduce the bug.
Indeed, we didn't cap upgrade levels because we weren't sure how much money people would make, and didn't have time to add more upgrades.