I posted this as bug… but Brecht say that this is not…
Now i search for solution to update strips without delete strips and adding again to sequencer…
http://projects.blender.org/tracker/?func=detail&atid=498&aid=30491&group_id=9
If changing a scene’s length made the scene strips longer they could interfere with following strips in the sequencer timeline. This would be bad. I think that you should have to update the scene length manually (and move following strips). Or try the script by Turi, you can change values for groups of strips at once or copy properties.