Hi Dirk,
This way it still does not work for GUI apps launched from the desktop environment (MATE in my case). I'm trying to add ssh keys via keepass2/keeagent (it doesn't see ssh-agent) and then use them in other GUI apps (Eclipse etc.)
strange ... it works for me.
keepass2 is started via
Exec=keepass2
in keepass2.desktop file; probably /bin/sh is not involved and so SSH_AGENT_PID is not set.