I have a btrfs RAID5 on 9 external USB3 drives. When I started the 16.04 beta1 Lubuntu live CD, the btrfs volume (named Backup) was mounted 8 times:
/var/log/syslog:Feb 28 00:45:51 lubuntu udisksd[2620]: Mounted /dev/sdk1 at /media/lubuntu/Backup on behalf of uid 999
/var/log/syslog:Feb 28 00:45:51 lubuntu udisksd[2620]: Mounted /dev/sdj1 at /media/lubuntu/Backup1 on behalf of uid 999
/var/log/syslog:Feb 28 00:45:51 lubuntu udisksd[2620]: Mounted /dev/sdi1 at /media/lubuntu/Backup2 on behalf of uid 999
/var/log/syslog:Feb 28 00:45:51 lubuntu udisksd[2620]: Mounted /dev/sdh1 at /media/lubuntu/Backup3 on behalf of uid 999
/var/log/syslog:Feb 28 00:45:51 lubuntu udisksd[2620]: Mounted /dev/sdf1 at /media/lubuntu/Backup4 on behalf of uid 999
/var/log/syslog:Feb 28 00:45:51 lubuntu udisksd[2620]: Mounted /dev/sde1 at /media/lubuntu/Backup5 on behalf of uid 999
/var/log/syslog:Feb 28 00:45:51 lubuntu udisksd[2620]: Mounted /dev/sdc1 at /media/lubuntu/Backup6 on behalf of uid 999
/var/log/syslog:Feb 28 00:45:51 lubuntu udisksd[2620]: Mounted /dev/sdb1 at /media/lubuntu/Backup7 on behalf of uid 999
ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: initramfs-tools 0.122ubuntu3 [modified: usr/sbin/update-initramfs]
ProcVersionSignature: Ubuntu 4.4.0-7.22-generic 4.4.2
Uname: Linux 4.4.0-7-generic x86_64
ApportVersion: 2.20-0ubuntu3
Architecture: amd64
CasperVersion: 1.367
CurrentDesktop: LXDE
Date: Sun Feb 28 01:02:46 2016
LiveMediaBuild: Lubuntu 16.04 LTS "Xenial Xerus" - Alpha amd64 (20160224)
PackageArchitecture: all
ProcEnviron:
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
SourcePackage: initramfs-tools
UpgradeStatus: No upgrade log present (probably fresh install)
I have the same thing, with a primary mount at /media/barak/foo and duplicate mounts at /media/barak/foo1 and /media/barak/foo2, where it is a two-disk btrfs filesystem. I can umount the extras and things still seem okay.