the depth of field is VERY thin at f/1.8 ...i doubt its motion blur. MF/AF shouldnt affect it either.
make sure your shutterspeed is up.. not less than 1/50th of a second.
what you are seeing is not motion blur, it is that most of your picture is out of focus and only a thin sliver is in focus. try f/2.8 and you'll see a difference.
http://digital-photography-school.com/aperture
this should help you understand aperture/DOF a bit more.