Not true. The status of all the game's switches are perpetually recorded in your save file. If you turn Self Switch A to ON, then save and quit, Self Switch A will still be on when you get back. The same goes for normal switches and variables.
The only way a switch would reset if you leave the room is that you have some other event to turn that switch OFF, and accidentally trigger it each time you leave. Normally, switches stay the way they are.
It should go like this; I'm skipping the graphic stuff for ease of typing.
@> Show Text: You got a Broom!
@> Change Items: [Broom]+1
@> Self Switch A = ON
And then make a second page. Set it so that page will only be active if Self Switch A is ON. Then you can do whatever with that page.
@> Show Text: It's empty. Crazy.