BizTalk duplicates files in FTP receive adapter.

I ran into the problem of BizTalk duplicating files during FTP transfer, which caused a lot of grief on my side. I thought, our partners were dropping duplicates onto the FTP server, but it turned out BizTalk was duplicating them, during transfer if the file was still being written on the FTP server at the same time as BizTalk tries to pick it up.
It is still rather unclear on behind the scene of how this is happening, but this is something that needs to be addressed. Either by enabling Service Window in the BizTalk FTP receive port, or by storing data in temp file while writing out to FTP, and then renaming it for BizTalk pick up as the last step of the process.