using "preOpenStack" in card script

[Sannyasin Brahmanathaswami]

if we put

on preopenStack
answer "hello" with "OK"
# do stuff here
end preopenstack


into the script of card 1 of a stack

As a way to encapsulate the preopenstack from the message path

and you put a button "Run" on the card:

on mouseUp
  preopenStack
end mouseup

click the button and you get the dialog, but it is immediately followed by a script error with the script editor breaking on the "preopenstack" line of the button

button "Run": execution error at line 2 (Handler: can't find handler) near "preopenstack", char 1

What's happening?

BR