Question: Maple objects display precedence in graph? (foreground/background)

Hello all,

This is my first time posting here; I usually find answers to all my questions by searching patiently but I was unsuccessful with this particular issue.

I attend an introduction Maple class and i'm building an animated bike as project. I was already rather comfortable with Maple so i'm trying to show off a little by adding lots of cheesy details to the scene, even if unnecessary. However, some objects such as the sky, which i would like to be in the background, are hiding parts of the bike.

I tried many things but i just can't figure out how Maple decides which object will be over others. I thought it was the order in which the display sequence is called but that doesn't seem to be the case. Maple’s display precedence just looks totally random to me. Polygons seem to cause the most problems.

Here's an example (try not to laugh at the scene :P):

I've set the blue background to be half transparent but it shouldn't be. In this animation, the bike's bench (an ellipse) and the sun (a disk) are both completely hidden the blue sky (a polygon) and the rainbows (circles) are also hidding the bench when the bike rolls in front of it. Is there a way to change that so that the blue polygon is behind everything? Why are the bench and the sun the only objects causing this problem?

Here are the commands for the bench, the sun, the background and the final calling sequence for everything:

(background is back2, bench is siege and the sun is soleil6)

Thanks in adavance! I hope there is a solution to this!