Panic: file istream-seekable.c: line 226

Hi, I have a lot of Panic in my logs. They happen almost every day and never on the same user. When it happens, the mail is not distributed (it's always lda). I discovered it because my Sympa server had a lot of users in error. The last error (below) was a local user sending a mail to 10 users :

Panic file istream-seekable.c

bose_proctitle = yes protocol lda {   mail_plugins = fts sieve   syslog_facility = local2 } -- Eric Mauger | Administrateur système et réseau IGF UMR5203 | https://www.igf.cnrs.fr