Thank you for the reply Andi. I'll perform some of these troubleshooting steps this evening when I get home from work.
I did double check the basic and advanced view to make sure CC1 wasn't controlling something I wasn't aware of. And in the case of my clarinet channel/staff Velocity XFade is using CC2 (default) and is actually off. I think this simplifies the test a bit. I also have Velocity+CC11 for dynamic control.
But what I'll do when I get home is set expression to something other than CC11 and see what the results are.