strange interaction with message box

[Andre.Bisseret]

Bonjour,
Often I have navigation buttons on the cards of my stacks (prev, next,  
first) ; often too I use visual effects as
in this example of a script of a button :
on mouseUp
    visual effect scroll left very fast
   go next
end mouseUp

Now, for one month or so, if the message box is opened, the visual  
effect occurs on it, not on my stack  :-((

On the stack, it goes to next card (or prev etc) as expected, but  
without any visual effect !

The visual effect occurs on the stack only if the message box is closed.

What am I doing wrong ?

Thanks in advance for any idea

Best regards from Grenoble
André