stack script executes when opening substack

[Jim McNeely]

Another newbie question; I appreciate the patience and help.

I have this attached to the main stack:

on preOpenStack
    put revOpenDatabase("mysql", "localhost", "blechy", "account",  
"pw") into MySQLID
    answer "MySQL connection ID: " & MySQLID
end preOpenStack

THEN, I have a button which is supposed to open a substack window  
thusly:

on mouseup
    go to stack "PatientFind"
end mouseup

When it opens PatientFind, it executes the main stack's on  
preOpenStack script, and then, if you close that window, it wants to  
know if you want to save the changes to the whole file.

What's up with that? I've read all the documentation I can find about  
stacks and substacks and cards and such, and none of it hints at this  
behavior.

TIA,

Jim McNeely