The Head Covering Movement. I was searching out something else, and landed on What Did Martin Luther Believe About Head Covering? In the link, the author says, "Luther did not see covering as optional." Of course, it might simply have been the case that 16th Century custom played a part with what's going on here.
The source for the Luther material was taken from Susan C. Karant-Nunn; Merry E. Wiesner – Luther on Women: A Sourcebook (Cambridge University Press, 2003). The authors have included a portion of Ein schöner Sermon . . . von dem Ehestande (Sermon on the Estate of Marriage) [Jn 2:1ff] (15 Jan 1525), WA 17.1:8-12. this sermon is scheduled to be translated in full in a forthcoming edition of Luther's works. Till then, here is the snippet from Luther on Women. Decide for yourself if Luther is arguing Christians wives must always have their heads / hair covered:
For what it's worth, the comment section of the blog post in question has some interesting debate.