An app being able to declare some operations to perform on the clipboard (overwrite, append, etc) that don't return any information about the contents are not a problem from a privacy or security perspective. At most they can be annoying.
I wouldn't expect that most people would double-check to make sure a series of gibberish characters matches what they expect, especially if they don't have any reason to suspect that paste wouldn't output exactly what they copied a moment ago.