Is there a reason why using --enclose or --wrap adds a question mark as the first element of the sources property of the source map?

I ask because, go ahead and laugh, I'm debugging in IE 11 and the presence of the question mark breaks the debugger view, showing me the uglified script with the message

Could not locate http://path.to/scripts/? specified in source map http://path.to/scripts/scripts.js.map.

I have a workaround that involves beautify, but I'd much rather have the source maps.