osm2pgsql out of memory on update

Hi, I've successfully imported the whole planet and the rendering works (slowly, but that's another problem). I've tried to update using the openstreetmap-tile-update-expire script, but it keep using all the RAM available and been killed, despite the fact that I'm using flag-nodes and that I tried to limitate the RAM usage with the -C option. I have 32Gb of RAM + the same in SWAP, so it doesn't make any sense to me. I've tried the -C option with only 8gb and the same append, it seems this option is not working as I expected.

The exact command used:

osm2pgsql -a --slim -G --hstore --hstore-match-only -S /path/to/my/script --flat-nodes /path/to/flat_nodes.bin -e13-20  -d gis -C 8000 -o "$EXPIRY_FILE.$$" $CHANGE_FILE

I've watched it working while monitoring the RAM usage, it's working fine at the beginning but as it progress, it's using more and more RAM, probably a memory leak somewhere but I can't find where and why... The RAM usage inscrease until it reaches the maximum, then after "Left to process: 6221" the process was killed.

Does someone have any idea of what's appening?

Thanks.