pFirstLineContainsHeaders is being ignored in DataGrid

[Roger Eller]

According to this datagrid lesson, this should work but it does not.  Could
someone please confirm?

http://lessons.runrev.com/s/lessons/m/datagrid/l/7309-how-do-i-populate-a-data-grid-with-data

on mouseUp
   answer file "Select a Tab Delimited text file:"
   set the pFirstLineContainsHeaders of grp "DataGrid" to true
   set the dgText [ pFirstLineContainsHeaders ] of grp "DataGrid" to URL
("file:" & it)
end mouseUp

The headers remain as "Col 1"  "Col 2",  etc.

~Roger