Version:            (using KDE 4.3.2)
OS:                Linux
Installed from:    Gentoo Packages

When opening mailto links that contain an ampersand in the body value, like

<a href="mailto:someone@example.com?subject=Test&body=Hi%2C%0A%0Athis%20is%20a%20test%20%3Ca%20href%3D%22https%3A%2F%2Fwww.example.com%2Fetc%3FParam1%3D123%26Param2%3Dabc%22%3ETest%20URL%3C%2Fa%3E.%0A%0AThanks.">Mailto link</a>

the pre-written mail body in the mail application that opens is cut off at the ampersand.

While the mail composer window should contain

-------
Hi,

this is a test <a href="https://www.example.com/etc?Param1=123&Param2=abc">Test URL</a>.

Thanks.
-------

it only contains

-------
Hi,

this is a test <a href="https://www.example.com/etc?Param1=123
-------

(for a clickable mailto Link go to http://p173.de/t/mailto-test.html)

This happens both in Konqueror and when passed to kde-open (for example from Firefox). Passing the URL directly to KMail works fine.