Text in an edit field disappears after opening a substack

[Charles Szasz]

I am using LC 5.5.5.  I have a substack (“Grade”) that is launched when the user goes from one edit field to the next field. The substack has a grade option button that inserts a grade in the second field. After the user enters text in the first field and goes to the next field, the text in the first field is cleared as the substack appears. 

This is my script for the second edit field that launches the substack:

on openField
   if field "grade2" is empty
   then
      go stack "Grade"
   end if
end openField

This is the script for the substack:

on preOpenCard
   set the label of button "grade" to "Select Grade"
   set the backgroundColor of this card to 202,202,202
end preOpenCard

There is no script in the first field.

Has anyone encounter this problem?  

Charles Szasz
cszasz at mac.com