InfoPath Dev

Hi, we have a form where users will enter the first and last name, and that name gets displayed as a filename in the Form Library.  I would like to have these filenames look like this:

Formname - Smith, Joe

Notice the comma after the last name.  Currently, when I do this, the comma is replaced with an underscore.  Is there a way to replace this with an actual comma?  I'm using this formula in my Submit Options:

concat("Form Request - ", my:LastName, " ", my:FirstName)

...but I have to currently leave a space between the first and last name which is visually unappealing to me.  My kingdom for a comma!!!!

Thanks to anyone who can help.

 I think this is default behavior in SharePoint because the form name is used as part of the URL to open the form, and you can't have a comma in a URL. One alternative is to have a promoted field/column that displays Smith,Joe, but have the link (filename + URL) happen on a field that does not have the comma. Good luck!

Thanks, I will not bother with the comma.  Maybe a dot would suffice.