I have the same problem.I hope it would be fixed soon.
# /var/qmail/bin/qmail-qstat
messages in queue: 3
messages in queue but not yet preprocessed: 0
# ls -la /usr/local/psa/handlers/spool |wc -l
2155
# du -h --max-depth=1 /usr/local/psa/handlers/spool/
46G...