Mailto issue in IWP script

I have a script in an IWP solutions that sends an email using the users own email client by calling a "mailto:" URL. The Open URL step looks like this:

"mailto:" & Email &

"?subject=" & Subject &

"&body=" & Field1 & "%0A%0A" & Field2

When I paste the result of this directly into a browser the I get an email to the recipient in the email field, a correct subject, and a body that reads:

"contents of Field1

contents of Field2"

However, when I run the script with Filemaker the body of the email comes out like this:

"contents of Field1%0A%0Acontents of Field2"

Why is there a difference when the URL is called from a script? And, of course, how can I fix it?