[Dovecot] Subscription problem with various clients

[Lucky U]

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