Why does it do this?

Ok I have a sprite and a mesh the mesh is in front of the sprite. I want the sprite to fade out. So I use a for next loop with entity aplha to fade it out. The sprite fades out just fine but the mesh in front of it also disapears for a second when the sprite is fading out and then the mesh fades back in to normal. But I never gave the mesh a enityaplha command. Why is it doing this?
heres the code. note I added the Entityalpha for the mesh to see if it helped and it didnt.

			For i# = 0.99 To 0.00 Step -0.01
				EntityAlpha backsprite,i#
				EntityAlpha stagemesh,1
				Delay 100
				RenderWorld()
				Flip 
			Next 

Ok I moved the sprite 0.1 more spaces back and now it works but I will still like to know why it did that.

Perhaps more code would allow us to understand whats happening. Just the code above doesnt give us enough information.

Id guess it's a Z-buffer issue, where the objects were too close together for the scale used.