Using wxMaxima 13.04.0 on Mac OS-X. The following integral fails:

integrate(log((x-a)^2+(y-b)^2),x)

it fails for non-zero y-b, and it fails to clean-up for y-b=0 (the integral would be correct if y-b=0 were substituted and cleaned up)

Note that the integral is correct for the somewhat simpler (yet logically identical) problem:

integrate(log((x-a)^2+y^2),x)