Here is a video showing the problem I'm encountering.
And here's my room change code:
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This behaviour happens because the game is rendering any frame without "cleaning" the previous one first, and your level view doesn't cover the whole screen (there are some transparent/translucent parts).
To solve this problem, you can either set a background or tell the game to clear the display buffer before drawing:
Clearing the buffer will fill it with a tint, after which object rendering takes place.