Version: 0.1.3.4 (and from comments previous version too)
Server: CentOS 5.4
Files are uploaded on server OK, but downloading them corrupts data (file extension does not matter).
Opening downloaded file in hex editor, reveals, that first 2 bytes are always added as newline - 0x0D 0x0A (but file size is correct - so last 2 bytes are stripped).
For bigger files there was some more mangling (size the same).
Also, please add this for rar files:
case 'rar': return 'application/x-rar-compressed';