This is actually a question or a feature request 
What want is import a hi-res mesh into zbrush and then store a morph
target of the untouched model, tweak it and then something like
Normal/Displace map --> Extract from morph target and this way
zbrush creates those maps with the differences between original and
tweaked without using model subdivision.
The reason for this is that my pipeline is with MAX and subdivision in max
(turbosmooth) is different than Zbrush uses (Catmull-Clark?) and the other
problem is the UV distort caused by zbrush ,totally different with max).
May be there’s already a workaround for this i don’t know yet.
Another question i have is why subdiv levels in zbrush modifies the base mesh (level 1) even without any additional tweak (try any mesh subdiv about 5 or
6 levels, go back to level 1, delete high subdivs and repeat the subdiv/delete
higher a few times and you will see the base mesh is smoothed and UVs distorted).
This is not a critic, just a request / question.
I am totally in love with Zbrush!!!
Greetz from Uruguay
EL |) /\ // )/
Example pic:
