layouts are not honored some times

I have a core20-based snap: https://git.launchpad.net/~snappy-hwe-team/snappy-hwe-snaps/+git/network-manager/tree/snap/snapcraft.yaml?h=snap-20

On an Ubuntu Core 16 qemu-system VM, if I install a previous version and then this version on top, layouts do not work as expected anymore:

$ snap install network-manager --channel=1.10/beta
network-manager (1.10/beta) 1.10.6-6 from Canonical* installed
$ snap install --dangerous /home/network-manager/network-manager_1.22.10-1-dev_amd64.snap
network-manager 1.22.10-1-dev installed

$ sudo snap run --shell network-manager.networkmanager
# ls -l /var/lib/NetworkManager
total 0
# exit

$ ls /var/snap/network-manager/x1/var/lib/NetworkManager/
NetworkManager-intern.conf internal-9c94a0f3-ec17-3d0c-b8c3-f60d2916c30c-eth0.lease seen-bssids
NetworkManager.state secret_key timestamps

$ cat /var/lib/snapd/mount/snap.network-manager.fstab
/var/snap/network-manager/x1/conf /etc/NetworkManager none rbind,rw,x-snapd.origin=layout 0 0
/snap/network-manager/x1/usr/lib/NetworkManager /usr/lib/NetworkManager none rbind,rw,x-snapd.origin=layout 0 0
/var/snap/network-manager/x1/usr/var/lib/NetworkManager /usr/var/lib/NetworkManager none rbind,rw,x-snapd.origin=layout 0 0
/var/snap/network-manager/x1/var/lib/NetworkManager /var/lib/NetworkManager none rbind,rw,x-snapd.origin=layout 0 0

$ sudo cat /proc/$(pgrep NetworkManager)/mountinfo | grep /var/lib/NetworkManager
553 585 8:3 /system-data/var/snap/network-manager/x1/usr/var/lib/NetworkManager//deleted /usr/var/lib/NetworkManager rw,relatime master:7 - ext4 /dev/sda3 rw,data=ordered
560 913 8:3 /system-data/var/snap/network-manager/x1/var/lib/NetworkManager//deleted /var/lib/NetworkManager rw,relatime master:7 - ext4 /dev/sda3 rw,data=ordered

In normal circumstances, the '//deleted' string does not appear in mountinfo. I have seen this while running spread test on the qemu VM.