surface split problems

Dear All, 

I am trying to cut out circles from my surface, which has ended in some unusual results for me - the circles split, but on two separate surfaces? I am repeatedly having this problem and no idea why - at the moment I am cutting each surface in half then stitching the two back together in rhino! Can anyone explain this for me?

On a side note, I'm rather surprised to see that a singular surface comes to roughly 1.5 MB (I have 80 of them to do!!) - is that normal? 

Many thanks in advance.