LF2 2.0a Crashes but 1.9c doesn't

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That did surprise me O_o. I can't see a reason for why they changed the limit, but it simply exists because objects are stored in a container that only allocated memory for 400 on-screen objects. Sometimes, you can exceed the limit by a number or two, but this will often cause random behaviors.

Does LF2 ever delete the objects in memory once they "fly off" the screen and are sure to never appear again?

The limit wasn't changed. The check to see if it was exceeded was removed.
To be clear the limit that was changed from 1.9 to 2.0 was the limit of loaded object data files, not the amount of objects currently in the game which remains 400.
This may be possible to patch somehow. I'll write a post if I can fix this.

Oh, I see. And that would be awesome if there is a patch to this. Would help a ton.