Huge performance drop caused by Background Objects?

For some reason, the background objects in the game I'm working on seems to cause a severe performance drop. My game is set up so that external graphics are loaded into the animation frames of an Active object upon the start of the frame. The Active is then positioned, the frame forced to the corresponding image, and blitted as a background object using "Add Background".

When I disable this event, or just deletes the Force Frame-action so that all the created Background Objects display the same image, the FPS rate goes up from around 160 to 360. This is very frustrating and just doesn't make any sense to me. At first I thought it was the fact that the images were loaded from an external source that somehow caused it, but the impression I get now is that just the presence of two or more background objects with different images is what causes this huge performance drop. Could somebody please explain to me why my game is acting this way, so that hopefully I can find a solution or a way to work around it?

Never mind - I figured out the reason for the performance drop was that I hadn't developed a system for continuously deleting old background objects, so they would keep getting stacked on top of each other and take up unneccessary space. I've fixed the problem and now my game runs much more smoothly.