12
Ok, I have solved this myself now.
In the Template manager, edit the profile_userinfo.html template in the the Extended Profiles section.
Above:
<input type="button" value="<{$lang_editprofile}>" onclick="location='edituser.php'" />
Add:
<input type="button" value="Change Password" onclick="location='changepass.php'" />
Admitted, not so elegant without the right smarty, but couldnt figure out what it is. <{$lang_changepass}> didn't work.
Remains the question why the button disappeared... Perhaps it was relocated?