Just got home from work. Plugged the cam in using an older (original) cable and with the laptop running off mains power.
The DMK is humming along
So, it appears the laptop's not happy when it's running off its own battery.
As Rae has pointed out, that's baffling. The DMK has its own separate power source.
I can only assume it's an on-board power management issue which creates a conflict with the camera?