Well thats where you see the difference between learning/studying Japanese and growing up with it.
I, too, have grown up with it so I'm rather bad at formal speech. And my writing/reading skills are that of 1st/2nd grader in Japan...
But still, I went to Japanese classes for 1 semester and they thought us both forms of "Sumimasen" (Sumimasen and Suimasen).