unlock screen doesn't unlock screen

[jbv at souslelogo.com]

Hi list

I have the following loop :

  lock screen
  repeat 20000 times
    -- do a lot of things
    unlock screen
    put myVar into fld myVar
    lock screen
  end repeat

The purpose is to lock the screen so that the heavy data
processing inside the loop isn't slowed down, but also to
display the content of myVar at each iteration of the loop.
But the content of the fld doesn't refresh while the loop runs,
only when the loop is over... I used to do that with HC, MC
and earlier versions of Rev and it used to work...
I'm on OSX 10.5.5 and LC 6.5.2
Any idea ?

Thanks
jbv