I think the general simplifier for abs does some things that it shouldn't. Example:
(%i1) abs(log(x));
(%o1) sqrt(log(abs(x))^2+atan2(0,x)^2)
Surely, (%o1) causes trouble for limit, integrate, solve, ... Another problem with (%o1) is
(%i2) subst(x=%i,%);
(%o2) sqrt(atan2(0,%i)^2)
Rectform and related functions will *not* simplify %o2 to %pi/2. Changing log to plog and all is well:
(%i4) abs(plog(x));
(%o4) abs(plog(x))
(%i5) subst(x=%i,%);
(%o5) %pi/2
A related bug (maybe this is more of a problem with carg, not abs)
(%i6) declare(z,complex);
(%o6) done
(%i7) abs(log(-z));
(%o7) sqrt(log(abs(z))^2+(carg(z)+%pi)^2)
Wrong: Should be 0, not 2 pi:
(%i8) subst(z=-1,%);
(%o8) 2*%pi
(%i9) abs(log(1));
(%o9) 0
Barton