Emu XL-7 & MP-7 User's Group

I am having some problems using standard midi files with my XL7. 
Specifcally, if I upload a file to my computer, and open it in Sonar, 
and then save the file, without even making any changes, the file is 
now different in size and content. What is really strange about this 
is that the original file that I upload, if I look at it using 
Eloader, does not appear to contain all the information (all the 
tracks and events) that I know are in the file.
Any help or ideas greatly appreciated.
thx
Dana