Found other bugs: Cannot use Start or check points in the second room, Mario will instantly die. Expended Vertical Levels will have a white background in the bottom. Thowmps/Falling Rocks/Cheep Cheep, and even water can still be visible/heard even if they're in the second room.
And if you are creating custom/using one normal background (not cave, volcanoes, athletic (9-1, sunset etc.), castles), in the vertical levels only the first 640pizels will be affected by the background, the rest of the level will have the background white.
-The hammer Suit doesn't work properly underwater. -The blue right underwater tile can be stacked causing the block counter to increase rapidly. -Foregrounds and Overbackgrounds in Section 1 will disable, if the player goes into Section 2 and then goes back to Section 1. -Any kinds of fish from Section 1 will disappear, while editing the level, if the player goes into the second section. -The Centipede platform will disappear in Section 2. -Giving a specific roto-disc a mark, which makes it rotate in a shape, can affect other roto-discs without a mark. -When a blue para-koopa collides with solid objects from below, it does a double-jump. -"Stop to Left" and "Stop to Right" marks are broken. -The "Missile Bill" mark does not work for upside down horizontal cannons.
If put on bottom white screen and other top gray screen then fill all white screen. Because you complete a level with that size Width X:20000 that mario goes to the right side of the screen and then happens that appears section 2 then and crash game. other values additional cheep cheep cannot show because to test level everything is neat. while the other is all neat.