Just to clarify on #1, it's not necessarily a difference in room dimension but in the view_port settings as well. Though it doesn't really matter which of these two it is as, like infern0 said, the only way to fix this would be to correct the source file.
While some people are lazy and simply write 800x600 as the size of the room, this is an approximation that doesn't account for the 8 pixels extra you need on the height of the room to make it fit a 32x32 grid perfectly. As such most engines are built around the 800x608 resolution as you don't get the annoying clipping of the last row of blocks, but some game designers simply assume the dimensions are 800x600 and make new rooms using that, which can cause the screen to jump slightly. Additionally, the default room size is 640x360 (I think) and some designers simply forget to change the dimensions, especially when creating bosses that don't need massive rooms and also won't adjust the view_port settings meaning the window changes size.