Stuck in "Background" window

[Ken Norris]

Well here I go again. This thing keeps ending up in the stack's background
window instead of the card window.

on mouseUp
  set the defaultFolder to "Doggies"
  answer file empty with filter "JPEGs,*.jpg"
  lock screen
  import paint from file it
  set itemDel to "/"
  cut image (last item of it)
  start editing group "myImageGroup"
  paste image (last item of it)
  send "stop editing" to me in 20 milliseconds
  open window "Practice1" -- **Even with this
  unlock screen
  send "choose browse tool" to me in 20 milliseconds
end mouseUp

...any ideas?

TIA,
 Ken N.