I'm new to this version of Sonar (last was back in 2006), and new also to session drummer.  I've had good success, but recently ran into a problem that I can't seem to solve.
 
Everything is fine with creating the appropriate instrument tracks (split as midi/audio).  I then use the step sequencer to create my pattern.  I place the pattern to begin at measure 2.   If I then play the song, I hear silence for measure 1, and the drums come in as planned on measure 2.
 
If I then grab the right handle of the drum clip and drag it right (to repeat/extend it), it appears to do so properly in the track view.  However, when I play the song the drums begin on measure ONE, when they should still begin on measure 2 (I only dragged to the right, not left).  There is no evidence of any events in measure one in any track.
 
This continues to happen unless I shorten the drum clip back to one instance, or drag the multi-instance clip to measure 4.
 
I've confirmed there are no other bounces of the track or any other phantom clips elsewhere.  Muting the session drummer track mutes all drum sounds in this project.
 
The song's meter is 2/4, and the step sequencer is set to 2 beats, 6 intervals.  I've already googled this and set the "Set Now Time with Full Reset", but the issue still occurs.
 
I suspect I have some type of property set on the drum clip or have something on my timeline that is causing it to think it needs to be playing in measure 1 when it shouldn't be.   As I said, I'm new to this version of Sonar and the navigation is somewhat intimidating.
 
Any help would be appreciated.  Thank you.
 

I tested your steps, but couldn't re create it - after extending / repeat the drum pattern to right.. The drum still starts at measure 2.
 
Any possibility to record a simple video showing the issue ?
 

Hi. This is just a guess, but it the play button in Session Drummer (when the interface is open) active, and set to sync to host? If so that could be your issue.
All the best.

I do not know how to set the session drummer to "sync to host", and the play button was not pressed on the SD interface (step sequencer). 
 
UPDATE:  The issue was somehow tied to another track that was mapped to TTS-1.  No matter what I did with that track (muted, moved the midi, etc), the drums still started on measure 1.
 
When I completely DELETED the TTS-1 tracks (it was a folder with 2 midi + 4 audio), the problem stopped.
 
I then re-added the synth, re-recorded the midi and it all worked as expected.
 
Prior to deleting the TTS-1 midi track, I looked to see if there were any events that could have been triggering the SD -- but didn't find any.
 
This is a mystery to me.  Fixed now, but not solved.
 
So far, I have not been able to duplicate it... 
 
Questions:  Could I have set something on the earlier TTS-1 or Session Drummer in the synth rack that caused this?  (I did repopulate all the synths in the rack)...
 
 

never mind
 

Maybe try adding your MIDI out to a MIDI device, if you have one. It should stop TTS from being initiated when no output is selected on a MIDI track (if I understand correctly).
All the best.