There is no end of song marker. Most times projects that go past where you think they should, there is some data way down the timeline. It can be an automation node, midi event or loop like the one you just experienced. If you want to assure the length of an export, in addition to selecting the tracks to export, select the time range. There are several ways to specify the time range. One way is drag across the timeline.

As far as plugins crashing x64, try installing 32-bit Sonar and working with those plugins there, as sometimes they do not load well into x64.  (talking about some of the 32-bit plugs).
 
Bob Bone
 

Could try jBridge as an alternative to BitBridge too.

fif4lifefif
+X2 seems to spontaneously change preferences on me, and I can't find where to reset them to my settings. For example, X2 used to return to where I started playback when I stopped playback. All of a sudden, one day it stopped doing that, which is pretty frustrating. I can't seem to find the option to change that preference ANYWHERE, despite the fact that in previous Sonar versions this was a simple tick-box in the Editing options dialog.

 
in track view:
options (menu) -> on stop, rewind to now marker