Bug in headers' UTF-8 encoding ?

hello all,

I make some tests with RoundCube and I think there is a little problem with headers' UTF8 encoding:

I'm trying to send a mail with the subject: "c'est le printemps et bientôt l'été !".

If I choose iso8859-1 encoding here is the result:

Subject: c'est le printemps et =?ISO-8859-1?Q?bient=F4t?= l'=?ISO-8859-1?Q?=E9t=E9?= !

If I choose utf8 encoding I get:

Subject: c'est le printemps et =?UTF-8?Q?bient=C3=B4t?= l'=?UTF-8?Q?=C3=A9t=C3?==?UTF-8?Q?=A9?= !

which is not displayed correctly: only the first eacute is displayed. I do not know the utf8 encoding but it seems that two special characters in the same word results in bad utf8 encoding.

Christophe.