This behaviour is odd and unexpected.
 
I have a (guitar) track which I send 100% to an FX bus.  The bus has nothing on it, just playing straight to master.  The original track playback is not muted.
 
Is there a delay when sending the track through a bus that does nothing?  I would expect it to raise the volume of the track because it is doubling the output of one thing.  Yet the volume is lowered with phasing.
 
Can someone explain why this is happening?   Only thing I can think is that the bus is delaying the signal so that parts of it cancel with the original.  Why would the bus introduce lag, and is there a way to avoid this?
 
 
 
 

This seems to be a bug! (And a big one)
 
When the FX send is enabled prior to hitting play, the volume is doubled -- because the original track is playing and the bus adds to it.
 
However, when the FX send is disabled and reenabled during playback, the phasing is introduced.
 
To get rid of the phasing, I have to stop playback, enable the bus and the play.
 
Can anyone present a rational explanation for this behavior or should a bug be submitted?

It's probably a slight latency delay because of an effect either on the track or the bus that is causing one to be delayed just the slightest bit which causes an audible phasing.

Hit the PDC button to re-align the tracks. Better yet, read the documentation on PDC. Some non-SONAR effects change their delay dynamically, so PDC has to deal with a moving target.
 
SONAR was one of the first DAWs to align tracks with effects of different latencies correctly, and remains better than most in that respect. One of the reasons I switched to SONAR way back when was because it was impossible to do time-coherent multi-band processing in [other DAWs that shall go nameless]. But you need to understand how the process works to take advantage of it.

Anderton
Hit the PDC button to re-align the tracks. Better yet, read the documentation on PDC. Some non-SONAR effects change their delay dynamically, so PDC has to deal with a moving target.
 
SONAR was one of the first DAWs to align tracks with effects of different latencies correctly, and remains better than most in that respect. One of the reasons I switched to SONAR way back when was because it was impossible to do time-coherent multi-band processing in [other DAWs that shall go nameless]. But you need to understand how the process works to take advantage of it.

There are no effects on the track.  Its just a send to an empty bus causing the phasing. And the problem occurs when the bus is enabled during playback.  There is no phasing when the bus is enabled prior to playback.
 
Bug.
 
If the audio engine can't maintain phase alignment throughout that is a problem that at least needs to be looked at.

I suspect it's not practical to align the 2 tracks at runtime automatically, but it is an interesting question as to why. If some effect has delay compensation on it which would mean the current tracks would have to drop out in order to line up the outputs, it implies that this could be worked around (within the engine) by just delaying when the send starts operating. Maybe Sonar just fails to (or chooses not to) perform the relevant latency checks when enabling the send during playback.

Are there any other tracks that are using FX feeding the same bus?

Kylotan
I suspect it's not practical to align the 2 tracks at runtime automatically, but it is an interesting question as to why. If some effect has delay compensation on it which would mean the current tracks would have to drop out in order to line up the outputs, it implies that this could be worked around (within the engine) by just delaying when the send starts operating. Maybe Sonar just fails to (or chooses not to) perform the relevant latency checks when enabling the send during playback.

That makes sense, but as there are no effects, I would not think there should be any latency; the original track and the empty stereo bus should be hitting the master bus at EXACTLY the same time.
 
Maybe someone else can recreate this.

200bpm
 
There are no effects on the track.  Its just a send to an empty bus causing the phasing.

That doesn't matter. If there are ANY effects in the project, and one of them has latency, PDC will try and compensate. This compensation by definition has to affect all tracks to compensate for the anomalous effect, and may need to be refreshed periodically.
 
I will try to re-create what you are experiencing with a fresh project, and will report back

I'm still not clear if by "no effects" you mean no effects in the project at all, or just no effect on that particular bus or track. In any case, I wanted to try and reproduce it.
 
I created a new project and inserted a WAV file (not a groove clip) in a track that went to the master bus. I then added a send to that track, and the bus output also fed the master bus. If I kept the bus level constant and varied the track level, as I turned up the track level, the overall output became louder. It exhibited this behavior whether or not I enabled the bus before playback, or enabled/disabled the bus during playback.
 
If you can provide more details on steps to reproduce that would be helpful, because the above didn't reproduce.