Comment # 1 on bug 991037 from Takashi Iwai

Likely due to the behavior change in 4.7 kernel:

commit eedf265aa003b4781de24cfed40a655a664457e6
Author: Eric W. Biederman <ebiederm@xmission.com>
Date:   Thu Jun 2 10:29:47 2016 -0500

    devpts: Make each mount of devpts an independent filesystem.

    The /dev/ptmx device node is changed to lookup the directory entry "pts"
    in the same directory as the /dev/ptmx device node was opened in.  If
    there is a "pts" entry and that entry is a devpts filesystem /dev/ptmx
    uses that filesystem.  Otherwise the open of /dev/ptmx fails.
    ......

Adding Goldwyn to Cc as this is something in VFS.