Most of paragraphs with quoted-printable characters don't show at all. I see empty and almost empty messages, sometimes with empty sender and/or subject. This makes it impossible to read messages with quoted-printable characters. Unfortunately that makes most messages in my (and my customers') language. The problem appeared after updating the mail server's linux distribution. I do not want to downgrade it.
I tried SquirrelMail 1.4.22, the 20130603_0200-SVN.stable, and fetching from svn myself on the same day. My php version is 5.4.13, running on Slackware 14.0 32 bit. SquirrelMail is set to utf8, but setting to latin1 did not make any difference.