[Dovecot] Subscription problem with various clients

Hi,

I'm a newbie with dovecot but i managed to install it and it's running great except i have this weird problem when trying to subscribe folders. I can subscribe to one folder at the time (for example inbox + sent), but if i try to subscribe an other directory client (tried with outlook express 6, Mozilla Thunderbird 0.8, Iloha Webmail) automaticly unsubscribes other directories. I've tried to search a solution for this problem without success. Please help. I'm using Dovecot 0.99.10.2 on FreeBSD 5.0