sqrt gets simplified inconsistently



Hi,

Maxima says
    (C39) 1/sqrt(x)-sqrt(1/x);
    (D39) 0
but
    (C40) 1/sqrt(-1)-sqrt(1/(-1));
    (D40) -2*%I

This is inconsistent!

How is sqrt(x) treated in Maxima? I.e. is it multi valued (then it should be 
treated as a set) or is it single valued (e.g. the complex number z with 
Re(z)>=0 and z^2=x)?

Felix