Okay, I think I know why a lot of the bugs exist, but it'll take some explaining:
1. This has been fixed.
2. First off, the wording of this is very hard to understand, so here it is summarized: When you walk off a ladder, you can still jump mid-air.
Second, this is because climbing a ladder doesn't remove your ability to jump.
3. There was no protection put in place for when you go above a certain speed. This also means that if you get enough horizontal speed, you can clip though walls.
4. This is intended.
5. PICO-8 has a set limit to how much memory can be in one variable, and if a level tries to add too many objects (not blocks) to the level, it crashes.