How do I refresh a text box?

Question

Using Access 2003 sp3

I have a form with a comment (text box) field and a continuous subform with records containing cost data.
In the cost field of the subform I have an after-update routine that updates the comment field when someone changes a cost value in the subform.

To do this, in the main form I have a let property to change the contents:

Property Let update_comment(ByVal new_comment As String)
Me.comments = new_comment
End Property

The thing is, the comment box doesn't display the new information unless I click into it.
Is there a way to get the comment box to redisplay after the let property changes the contents?

Thanks in advance for any help.  --Fred