squatter issue on Cyrus 2.4

[Marco]

Hello,

  I have Cyrus 2.4 with thousand mailboxes and separated partitions for 
data and metadata, with squat files in metamaildata partitions.

Every night at 2 I run "squatter -s -a -i" to update the indexes.

Two nights ago a metamaildata partition filled out. Starting from 2am 
many GiB busy in few hours. I can't understand why. No errors in Cyrus 
logs. I didn't find the files which caused the busy space.

Last night squatter didn't reproduce the error.

Do you have ever experienced problems like this?

Thank you very much for every hints.
Kind Regards
Marco

******************************************************
name       : Cyrus IMAPD
version    : v2.4.17-Invoca-RPM-2.4.17-6.el6 d1df8aff 2012-12-01
vendor     : Project Cyrus
support-url: http://www.cyrusimap.org
os         : Linux
os-version : 2.6.32-279.el6.x86_64
environment: Built w/Cyrus SASL 2.1.23
              Running w/Cyrus SASL 2.1.23
              Built w/OpenSSL 1.0.0-fips 29 Mar 2010
              Running w/OpenSSL 1.0.0-fips 29 Mar 2010
              Built w/zlib 1.2.3
              Running w/zlib 1.2.3
              CMU Sieve 2.4
              TCP Wrappers
              NET-SNMP
              mmap = shared
              lock = fcntl
              nonblock = fcntl
              idle = idled

******************************************************
EVENTS {
   # Squatter
   squatter      cmd="squatter -s -a -i" at=0200
******************************************************
metapartition_files: header index cache expunge squat
******************************************************