Okay, should have done some more digging to start with. I've now found the description of my issue in the tutorial in this forum http://forums.scummvm.org/viewtopic.php?t=4144 and this describes my issue and the need to change the Graphics mode. The tutorial recommends NOT using the 2x mode and so I...

Whenever removing the scummvm.ini file, it will drop back to 1x, and you'll need to change to 2x. I can't explain why you've never had to do this before, but I have to do it every time I remove the scummvm.ini file on my 640x480 device. Well I did delete my previous scummvm.ini - wish I hadn't now!...

I just upgraded my 0.12.0 ScummVM installation on my HP iPaq hx4700 to version 0.13.0. Apart from there now being two executables, the only major change I have so far noticed is that when the Graphics mode is set to "<Default>" the entire ScummVM windows is the size of a small postage stam...