There's something in there somewhere. The way I found out the issue with two automation nodes placed "on top" of each other was opening up every track to see the automation.
 
Also, any tracks that are hidden will influence the length and won't be subject to cutting in the timeline. Bus automation can also cause this.

Like most things in Sonar there's always more than one way to do the same task. 
 
You can apply my method of using split to the whole project.
 
First go to preferences/ editing / Clips and  select  Right of split point
Now in track view focus on tracks, use Ctrl/ A to select all.
Put the Now Time at your ending. And right click on the top track keeping all tracks higlighted.
Select SPLIT and all to the right should be now selected
Delete. 
This works for me,,, I just tried it. 
 
dots in a track both midi and audio means there is data to the right somewhere. 

Cactus Music
Like most things in Sonar there's always more than one way to do the same task. 

Cool trick!

well,I set it to right portion, and it still deletes the data to the left...

dongreywolf
well,I set it to right portion, and it still deletes the data to the left...

Did you change the Left/Right portion in the Preferences dialog that Johnny mentioned?  Left is the default so you'll need to explicitly change it first so that the split leaves everything to the right selected.