I have a question in mind that i always question about 8-4 1st castle room about why the piranha plant that you will entering to go to room 2 always dissapear. I know Bismuth explain it on explaining in the "Smb speedrun explained" video but still i can't understand what he meant to that.

So can someone explain what really just happening in that scene.

In the process of looping the rooms, all enemies are cleared. On the NES it clears early, before the pipe, which makes the plant dissapeared.

So if i go past the pipe and the room reset the piranha plant was now in the pipe legitimately. And i notice on smb1 all satr speedrunners just wait because the coder of the game notice that mistake or something.