Disappearing Backdrops

This has happened to me before. I do not recall how I remedied what was going on; therefore, I am asking.

In a simple 640x480 level, there is foreground, a river, and a mock background that is just for looks. For some strange reason one individual tile of the background floor disappears immediately after the fade-in effect, leaving a red house sitting halfway on land and empty space.

First, has this happened to anyone?

Second, and more importantly, how do I fix this?

Its kind of hard to tell what is going on if you don't have the file.

Yes, this has happened. Sometimes, while scrolling, (and appearently frame trasistions too) the backdrop dissapears. This usually doesn't happen unless you paste an object into the backround though.