[horde] About default charset

[eugenio vota]

Anybody can explain to me how Horde switch over between the different charset available for the same language?

I installed exactly the same Horde 4.1.3 Imp 3.1.3 instance over 4 different server with UTF8 as default charset an 
it_IT preferred language. Now when I login to the different server from the same PC with the same bowser,
for two server I get the page UTF8 encoding, whereas the two others server respond with ISO-8859-1 charset.

The four servers have a slightly different version of Red Hat Linux, but each have "locale" support for it_IT and it_IT.utf8

As very noising side effect, now sending to me a message with UTF8 charset with one of the two server that got fallback 
to ISO-8859-1, I receive the warning box that the message is writed with a different charset.

Anybody know why?

Thanks all.