Browsed ftp.gnome.org and found out that NetworkManager 0.9.6 was released but was not announced on the first page.
Compiled this version with the Slackbuild provided in source and NetworkManager doesn`t segfault anymore.
Also a new version of nm-applet was available but NetworkManager 0.9.6 works just fine with nm-applet provided in -current.
From the changelog of NetworkManager 0.9.5
Overview of changes since NetworkManager-0.9.4
This is a new stable release of NetworkManager. Notable changes include:
* Many libnm-glib fixes, including crashes when NetworkManager restarts
* Enhanced IPv6 stability and compatibility
* Fix regression in carrier handling for devices that don't support carrier detect
* Add ability to connect to new WiFi networks from nmcli
* Add native support for ADSL modems using PPPoE or PPPoATM
* Reduce number of changes made to DNS information during connection setup
* Add support for IPv6-enabled VPN connections
* Add device driver version, firmware version, and autoconnect properties to D-Bus API
* Add on-demand WiFi scan support
* Fix IPv6 default gateway handling for DHCPv6
* Add Vala language bindings
It seems the segfault was fixed since 0.9.5