[Dovecot] quota.

Hallo. Sorry for may bad english. I'm running dovecot 1.0.15 on a debian lenny system. I've set quota plugin and, under section plugin, I've set:

quota = maildir quota_rule = *:storage=50M quota_rule2 = Trash:storage=10%% quota_warning = storage=95%% /usr/local/bin/quota-warning.sh 95 quota_warning2 = storage=80%% /usr/local/bin/quota-warning.sh 80. For some accounts the quota limit works well. When I send mail I receive a rejected mail for quota exceeded. For some other accounts it doesn'work despite they have passed the 50M storage limit. Why?