Limitations of FTP (file transfer protocol) and CurlFtpFS filing system
Filenames beginning with a . (period)
The developer of CurlFtpFS advises that some types of FTP server do not allow creation of file names beginning with a period (.).
If you copy from a rich filing system (such as HFS+, NTFS or ZFS, all of which support extended attributes of some sort) to a lesser filing system, then Finder may properly make use of ._ files to signify that a file is busy — for the duration of its copy.
If your FTP service disallows file names beginning with . then Finder can not do its job.
This is a problem with your FTP service — not a bug with Apple Finder, MacFUSE or MacFusion?.
Workarounds
If you're happy with the concept of lossy copying, then for problem situations (only) you might consider using an alternative to Finder.
