Comment 2 for bug 1377651

This isn't a bug in ufw, but rather something that needs to be tuned for your system. You might be interested in reading:
http://security.stackexchange.com/questions/43205/nf-conntrack-table-full-dropping-packet

It could be argued that ufw should have cleared the table when disabled, but this would likely result in more problems for people who disable ufw and not seeing this problem.