Maybe someone familiar with DROPS patterns can help.
A friend of mine in PA emailed me asking for help.
I nearly never use patterns anymore and my best guess was that "M.1" referred top "pick up horizontal yarn between 2 sts and knit twisted".
Here's what she wrote:
". . . in this case the M.1 was to refer to the little chart labeled M.1 in the pattern. It looked like you are supposed to do yarn over but I don’t see how you can do that without something in between. I think I just don’t understand the chart. . . "
Here's the link to the pattern she sent: