Just trying to isolate and maybe re-create the problem with this script. Im sure that some combination of show,hide,visible,show(n) will repro the problem (prob something to do with show(n), as that was last thing added.

code:
break on
 
$form = createobject("kixtart.form")
$form.caption = mainform
$form.fontname = verdana
$form.fontsize = 12
 
$button = $form.commandbutton("popup")
$button.center
$button.onclick = "pop"
 
$form.center
$form.show
while $form.visible
 $=execute($form.doevents)
loop
 
exit 1
 
function pop
 
 dim $popup
  
 $popup = createobject("kixtart.form")
 
 $popup.caption = popup
 $popup.witdh = 200
 $popup.height = 200
 $popup.center
 
; $form.show(0)
 $form.visible = 0
 
 $popup.show(1)
 
 while $popup.visible
  $=execute($popup.doevents)
 loop
 
 $form.visible = 1
 
endfunction