Transfer from FTP: when TC creates .bak copies of files which it overwrites?

[DrShark]

I tried several times to copy the file of few Megabytes in size from FTP to a PC where the same file already existed, and pressed Cancel at different time after the start of overwrite process: sometimes full copy of original file but with a .bak extension appeared in its folder on PC after pressing Cancel, and sometimes it didn't... The file with original name on PC had the data which was partially download from FTP.

A questions: under what conditions TC creates such .bak copies of original file?

[ghisler(Author)]

Only "Compare by content" creates such .bak files, FTP does not.

[DrShark]

Only "Compare by content" creates such .bak files, FTP does not.

I noticed that when TC creates such files during Overwrite operation when copying from FTP with F5, it seems it tries to delete these .bak files, but Windows doesn't always show/report to TC that they are deleted.
Sometimes when I press Cancel in overrwrite progress, if such a .bak file appears in TC's panel, I get Access Denied error on any kind of access attempt (including attempt to create a hardlink to such .bak file, or unlock it with Unlocker) on it. It seems such files disappear after Total Commander restart... Can you confirm that such a behavior can take place?