AOZ Studio V1 (TBD bugs clean/-> V2)

Hello Wizards;

I uploaded to AOZ a screen demo I was working on a Pre-AOZ engine, and there’s something wrong now with the manipulation of screen layers. It seems like it is inverted and jumping a number.
Can’t precisely explain what is happening so I made two screen recordings to demonstrate the issue.
The culprit code is a loop that move screen 1 back and forth between layers.

          screen 1 : 'scale and move up ball between screens
            Bob Scale 1,1/lyball,1/lyball 
            Bob 1,(mscreenHalfx-bobhalfsize),(mscreenHalfy-bobhalfsize)-(lyball*bobquartsize)+bobquartsize,1 
            're-arrange screen layers to move ball between layers
            for ly=2 to 4
               Screen to back ly 
               if lyball=ly
                 Screen to back 1 
               end if
            next ly 

I do a loop before this one, that position the screens in order and move it using Screen Display commands.
(Sorry for the sluggish screen recording)