Mc positioning wrong

I am using flash cs4 to create my flash files on macosx.

When testing the swf, everything looks good on macosx, but on windows, some of the mc’s are not in the right position. They are lower than on macosx,

They arnt off by much , but enough to make it look a bit poor.

Can anyone tell me why this would be? both are using the same flash player version.