Depends if the process that is writing to the file holds a lock on it (which it should). If it does, but is in a location where VSS can create a shadow-copy, SE might try to copy it using VSS, but you can tell SE not to use VSS if you want (in which case you would get 'file in use' errors: same applies if VSS is not usable, e.g. external drive, networked resource).
If there is no lock, any 'successful' copy of a partially-written Source file might corrupt (replace) a prior backup of such a file, yes.
You'd need to ask them?
If there is no lock, any 'successful' copy of a partially-written Source file might corrupt (replace) a prior backup of such a file, yes.
ThomasB wrote:I would like to know more precisely about eMule
You'd need to ask them?