This is a limitation of the HP synchronizer tool. When using the synchronizer When an attachment is updated and saved back into QC it needs to be given a new name instead of updating the existing one. The synchronizer tool is not able to update attachments with newer versions only create new ones, so when the size of an attachment changes (ie when you update the attachment in QC) it is treated as a new attachment. This can be found in the HP synchronizer 1.40 user guide this section can be found on page 71.