[Elecraft] K3 Diversity and mode changes

[Graham Kimbell (G3TCT)]

I'm playing with diversity operation and find that when I change modes say from usb to cw, the main rx changes frequency slightly to keep the received tone the same (as expected), but the sub rx doesn't change frequency.  
This is not a big deal because I can tap A->B to force the frequencies equal, but does anyone know if this is usual or if I have something set wrong?

f/w 3.77

TIA
Graham