Sorry, just talking to myself here, but I've just fixed it and it didn't require a services restart or iisreset. So in case anyone else has this problem, here's the "fix"...
On our Dev system (where it was working OK), on the Quick Launch config screen I had the "Active" checkbox ticked for all three Entity types selected in the dropdown. On Live I only had this ticked for "Call" (as that is the only screen we really wanted it displayed on).
However, it appears that all three checkboxes need to be ticked for this to work on just Calls. I have ticked all three on Live and it's now working correctly, so I guess it's a little bug in VSM that requires all three "Active" checkboxes to be ticked.