Qjail and listing ports to be updated.

I am using sysutils/qjail for my jails (qjail-5.0). My host system is: FreeBSD 11.0-RELEASE.

Normally I would fetch the hosts' ports tree:
portsnap fetch update

Then I would update the ports tree of the jails:
qjail update -p

I would normally then be able to list packages which could be updated using:
jexec $JID pkg version -l '<'

For actually updating the ports to be updated I'm using ports-mgmt/portmaster.

But now jexec $JID pkg version -l '<' does not list any ports or packages to be updated anymore. Though ports-mgmt/portmaster does detect ports and updates them.

When I run a one-time qjail update -P the listing of ports (and other packages) to be updated works as expected (note the capital 'P' which copies the entire ports tree instead of fetching just the differences and then updating).

Then after updating those packages and later on updating the ports tree again (trying the lowercase 'p' again) jexec $JID pkg version -l '<' fails again.

pkg version -l '<' for listing ports and packages to be updated inside the host system does always work as expected.

I would be glad if someone could offer any insight to this.