the reason this is happening is that Spry is a javascript framework.
ID's created for use by spry must conform to the javascript naming rules, and one of those rules is that the variable name cannot begin with a number.
In form builder, the element name is also used as the ID and in the Spry Span tags ID.
I will put though a feature request to add the ability to specify the ID for a form element as well as the name.