Sorta similar to the minus world in 1-2, but not really. All 3 pipes take you to the same place. IDK if I'm the first to discover this, but does anyone have an explanation for this?

I found this messing around with some game genie codes a few months ago. It’s kinda like smb2j where you can wrong warp back to the beginning of the stage

This has been known about for a long time.

Yeah this has been known about for quite some time. Also, if you enter one of the pipes before the warp zone is loaded and as you are going down the pipe scroll the screen so that the warp zone loads, the same result will happen but it will load the start-of-a-level cutscene before starting you at the beginning of the warp zone.

I find going down one of the pipes without the warpzone being loaded just immediately takes me to the beginning of the warpzone, I'm guessing it's because the game is confused, but I don't know how it works

I would guess that would be because the current warp memory would be the warp zone you were currently in, so the game just loads that zone after you take a warp

Probably

HappyLee's "maximum coins" TAS - he spends the whole time in 4-2 looping here to get coins