The problem seems to be line [784] of trunk/phpgwapi/inc/horde/Horde/iCalendar.php
$value = str_replace($this->_newline, '\n', $value);
When removing this line, the description value is correct on the client.
I could not find any sideffects during my tests, if some clients have
problems with this, I assume this would then have to be fixed at a higher
level, because the current state with this line just causes broken output.
From wikipedia regarding Linebreaks in QuotedPrintable:
If the data being encoded contains meaningful line breaks, they must be encoded as an ASCII CR LF sequence, not as their original byte values
Vcard extract without the reported line code:
DESCRIPTION;ENCODING=QUOTED-PRINTABLE:Desc 1=0D=0ADesk 2=0D=0A=0D=0A
Vcard extract with the reported line of code
DESCRIPTION;ENCODING=QUOTED-PRINTABLE:Desc 1\nDesk 2\n\n
pointed out by Philip Herbert. Carl Knauber Holding GmbH & Co KG
cb8cd0f3e6