Thanx for the work-around (smells like a bug though)
I have a dual monitor and a dual wacom set up (use an intuos 3 PTZ-630 mapped to both monitors for the ‘normal’ computer functions, and a Cintiq 21UX as my main art window) For several reasons I had my second monitor (24" dell) as the primary.
oddness was happening, as the intuos 3 was behaving normally in Zbrush (ie adding) where as the Cintiq 21UX was subbing.
Weirder still, touch the pen to the Intuos and then make a stroke on the Cintiq and the first stroke would add then all subsequent strokes would sub.
searched this forum and found the ‘Make the Cintiq the Primary monitor’ work-round.
Now the Cintiq works fine but the Intuous subs when it should be adding, also the ‘first stroke works fine after touching the other tablet but subsequent strokes don’t’ behaviour is not evident when the Cintiq is the primary monitor.
as I am running the latest drivers and no other program exhibits this behaviour I can only assume it’s a ZBrush issue.