Why does data sometimes duplicate itself on an Exel sheet when I S
 

I have created a shared workbook to use as a weekly phone log, using Excel
2000 (it has five worksheets within it). When I Save it, the program will
sometimes randomly duplicate lines of text within 1+ of the worksheets. For
example, it may automatically copy and paste the last ten rows at the bottom
of Monday's page, the last eight rows at the bottom of Thursday's page, and
leave all the other pages as is. The next time, it will save the entire
workbook as I want it. How can I get it to save and not randomly duplicate?
(I can delete the duplicated rows and save again, to get a corrected
worksheet, but it gets to be a pain).