Hi,
I have used the fish protocol with dolphin to connect to my second computer. I noticed very strange behavior of dolphin. Dolphin makes a local copy of the file from my second computer in the background without any notice. I was lucky because file is big 1.2 GB, I guess that dolphin is trying to do a copy for any possible future actions, like eg. preview or embedded playing (watching a movie in dolphin), Evidently such actions like background copy, without any notice, of remote files should be definitely not allowed. No idea what to do. I have an option "preview" in dolphin set for the files at most 2 MB, but this limit seems doesn't work for media files. How I may prevent dolphin for making any non-demanded copy or move files from remote computer? Such behavior in every way evidently harms security of the system. I am a bit too nervous at this moment ....

I can't say I've ever noticed this behaviour. Try using the sftp command via dolphin instead. See if the behaviour persists. e.g.

Hi, I noticed this behaviour only with .avi files. By default I use ssh2 connection.

sftp also uses ssh.