unexplainable error

I have Apache/php/PostgreSQL on FreeBSD, all latest stable versions.

Every time, after mass import into the database (it's a development
server, so the import updates the database with full dump from the
production server) - the first several clicks on the development web
site return -

PGSQL ERROR: FATAL: terminating connection due to administrator command
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.

After hitting few times the refresh button of the browser, all is back
to normal until the next import.

If the FreeBSD is restarted before that, the problem does not exist.

Could anybody advice on the possible reason?

Kind regards,
Iv