Zero Drops in Zipcode when copying over values

Hello

Hopefully you can help me out with this problem
I created a button that when clicked, will will populate the Shipping Information, if it is the same as the Billing Information.

My dilemma is that in when I populate the zipcode fields (which are special formatted for zipcode) with a zip's that begins with zero , I receive the following error: "the value enter does not match the format of the field [0.2.8-Ship to Zip]" (fyi both zipcode fields are formatted for zip)

When I remove the special zipcode formatting, the leading zero in the zipcode is dropped

Below is the javascript I am using.

//copy values if billing address is the same as shipping address
this.getField("0.2.4-Ship to Address 1").value = this.getField("0.1.5-Bill to Address 1").value;
this.getField("0.2.6-Ship tol Address 2 ").value = this.getField("0.1.4-Bill to Address 2").value;
this.getField("0.2.5-Ship to City ").value = this.getField("0.1.6-Bill to City").value;
this.getField("0.2.7-Ship to State ").value = this.getField("0.1.1-Bill to State").value;
this.getField("0.2.8-Ship to Zip").value = this.getField("0.1.8-Bill to Zip").value

Your help will be much appreicated.