Button to copy from textbox to textbox wont work after reopening access.

Hello All!

I have read some of the posts on how to create a button to copy an input from one textbox to another textbox, which were very helpful. It works fine at first, however, after re-opening access the code for that button no longer does what it originally has done before.

Scenario:
I am creating a customer form where fields for an address is present as well as a shipping address. When the shipping address is the same, a button will copy the original address to the shipping address.

Quickly, I have created txtF_Name and respectively txtS_F_Name where txtS_F_Name will duplicate data from txtF_Name if btnCopy is clicked.

Code for the button with the On Click Event simply is:
Me.txtS_F_Name = Me.txtF_Name

All works well on the first go around. However, after closing down the database and reopening it and the form, the copy button will no longer function. I am sure there is some kind of rookie mistake of mine, and afterall I am a rookie, but any ideas or solutions would be appreciated. Thanks for the help in advance!