Somone reported an issue, which might not really be true. Some password manager is apparently disturbed by kleopatra because it monitors the clipboard and if someone else other then the intended recipient application reads it then the clipboard gets empty.
This sounds really strange and messed up from a security perspective but after a quick glance at Windows Clipboard API I think this could be possible.
So I checked where Kleo actually uses the Clipboard and found no real reason. It looks more like someone intended to use something like "identify" on clipboard contents to automatically provide options like decrypt or something but then did not do this.