I use Evolution 3.6.4 on Fedora 18 x86_64, my main language is German.
I got a mail (on my imapx account) encoded in iso-8859-15 with the word "hügelig" in it. The mail is displayed correctly in evolution.
When I click on the search bar, search for "hügelig" in the message contents, I do not get a hit. If I change the search to "hgelig" (note the missing umlaut character), the mail is found.
If I force the display encoding of the mail to utf-8, the word is shown as "hgelig" in the message body.
So my guess is, that evolution only searches in utf-8 encoding and it does not respect the actual encoding of the message, at least not when searching.
Any idea on how to change that?