Stanislav,
Until the cabs/abs problem is resolved, there is a workaround for your
problem, namely to define a function which first calculates the complex
numerical value, and only then calls abs, something like this:
Instead of
plot3d( abs(f(x,y)), ...)
use
fff(x,y) := block([temp], temp: float(f(x,y)), cabs(temp) )
plot3d( '(fff(x,y)), ...)
Let us know if this helps.
-s