Comment 4 for bug 1593611

This is not a "flashplugin" issue as it happens randomly with some other packages when a script validate an upgrade. that one has not been updated to support the new apt design "'_apt'"

The real problem is : there is _apt user on the system

grep -B2 _apt /var/lib/dpkg/info/apt.postinst

 # add unprivileged user for the apt methods
 adduser --force-badname --system --home /nonexistent \
     --no-create-home --quiet _apt || true

 # Fixup any mistake in the home directory of the _apt user
 if dpkg --compare-versions "$2" lt-nl 1.1~exp10~; then
     usermod --home /nonexistent _apt