Work Item Templates do not appear to be working as I would expect.

I create a work item, and fill in the description and Planed for Fields to be what I would like.

Now, when I create a template I am asked to define Template Variables. The two variables I am offered are "Planned For" and "Files Against". My guess is that if I check one of these it will ask the user to specify a value for hat field *before* creating it. So, I leave them unchecked.

When I create an instance of the template, the description is filled out the way I want, but the planned for field remains unassigned.

Why was Planned for not taken from the template I created?