Hello from the UK! Finally got my system setup over here and ran into this issue where projects do not stop at end of song. I opened the SONAR demo bundle and at the end of the project, it keeps playing and a flat audio line is drawn on the master track as if it is recording something. 
 
There used to be a setting to stop playback at end of project/song, but I am not able to figure out where that is. Any help?

http://www.cakewalk.com/Documentation?product=SONAR&language=3&help=0x200C4
Options menu "Stop at Project End"

[Track view] Options > Stop at Project End
When this option is checked, playback will automatically stop after the last event in the project is reached. When this option is unchecked, playback will continue beyond the end of the project and playback can also be started in an empty project.

scook
http://www.cakewalk.com/Documentation?product=SONAR&language=3&help=0x200C4
Options menu "Stop at Project End"

you beat me to it in mere seconds

YEP! there it is, thanks!!

well, the demo bundle is still going on and looking as if it is recording a flat line. 
 
Something doesn't look right.
 
1. Open bundle for demo
2. press play
3. put spp to end of project+10 secs
 
My project still goes on and acts as if it is recording. 
 

Could be automation nodes or MIDI data to the right of where the end of the project appears to be.

...

restarted SONAR and made sure setting was active. It worked as expected this time. thx for checking guys!