=) This is very very common problem not only starcraft one but many starts from rataller 2 Revenge lol, when they come from other end of giant map ignore other almighty CPU on their way and try to pwn you, and few other games as well, warcraft inc, thats from about 7 yo ago reminds.
thats of course done deliberatly, coz cpu AI are too dumb and could never EVER match player