Why does this crash?

[jda]

I'm doing a query where I create and then destroy a sortmethod 
on-the-fly. It worked before, but now crashes (V4RB, b11, OS X):

       s = s + " ORDER BY authorEditorSortMethod,date" //create the query

       fld = 
myDatabase.myReferences.createField("authorEditorSortMethod", 
kv_TypeVarChar, 504, "English", "if
                (length(authors)=0, if 
(length(editors)=0,title,editors),authors)") //create a method in 
case a field is
                 empty


     myCursor = myDatabase.SQLSelect(s, kServer, kReadOnly) //OK

     if fld<> nil then
       myDatabase.myReferences.deleteField(fld) //destroy the 
temporary method -- crashes!
     end if

Obviously (?) Valentina has locked the new method. But why? Once the 
SQL query is done does the cursor have to know about the method used 
to sort the results?

Jon