I have a similar question posted.  I e-filed 2017 Michigan return.  I have a refund coming, but my electronic instruction filing printout also tells me I need to mail a signed return with all attachments.

My return was accepted by the State, soI think this may be a glitch with the instructions being printed.

I don't know if they monitor this Xchange, but it would be nice if they would check it out and post a response.