Massive signal spike when switching between Stereo and Mono on Master Buss

Howdy folks,
I'm not totally sure what to call the problem I've experienced other than what is in the title. I did search first but found nothing referencing my issue. Maybe you're not supposed to switch between mono and stereo while a song is playing but I didn't know that and I've never experienced what happened today - and been working with Sonar since Sonar 3. Not that I do it as a practice, but I often switch between mono/stereo on the Master Buss. During the process of mixing yesterday I used the Mono/Stereo button to switch back and forth to test a mix. Everything went fine. However, today I was mixing the same tune in mono, switched to stereo and over half the channels began spiking with an awful sound. I turned everything down, stopped the transport, and switched back to mono. I started the transport and the spiking began again. I rebooted my "dedicated to Sonar" PC and launched Sonar, then the same song. This time I set the Master Buss on Stereo before starting and it initially spiked, so I closed Sonar and reopened. With the Master set to stereo, this time things went smoothly as expected.
 
I'm at a loss - I would think this is a fairly standard procedure - why have a mono/stereo button then? Or I'm I missing something. Maybe it's time for a mono speaker - I'm sold on eq'ing and mixing in mono. I appreciate any feedback!

I appreciate the response! I am chagrined that I didn't check the online help vs. forum - thanks for the reminder. The spikes I heard and saw were certainly more than 3dB and very "non-musical". I'll check to see if Input Echo was enabled on some tracks - I bet so. And if so, I guess that could have caused a feedback loop? I wonder why the spikes are intermittent. I can play a project for an hour, switching back and forth between mono/stereo, and not have any spikes. Then "BAM". Huh.
 
Thanks again.