Read the thread from the beta forum here:
community.sophos.com/.../75611
So far no critical issues on my SG105w... Still can't bridge the internal wireless to my LAN but that's been an issue for a year now.
We are using many SG105w and only had the issue you describe once long ago. Since then we have used it many times with bridging the ethX with the wlanX interface.
Did you try the workaround I developed?
Cheers - Bob