Dave
I think the problem is they are deleting so many posts at the same time that new one's are being added, the database is finding it hard to catch up.
Plus the bigger the thread the bigger the issue as a huge thread existed in Jet Blast that was having page numbering problems and as soon as a new thread was started, they went away.
Also, the Deputy senior mod gave a good explanation in a thread in JB on why they deleted certain posts at certain times in MH370. Worth reading.