File Overwriting On Upload Unreliable At Present

[tamjk]

I'm using version 3.50.0 for updating website files on the server.

At present I can't rely on FileZilla to overwrite files reliably.
The only sure way to do so is to delete the existing file on the server and then upload the new one.

Sometimes the first "Update" click on the client-side file has no effect at all.
More times there is a change to the date of the server file but it still is not the same size as the client-side file.

Surely, an overwrite ought to be total - and totally reliable.