under Windows it is demanded, that applications
SHOULD NOT overwrite the clipboard by themselves.
Apart from that, in some cases my idea might be
When double clicking a password or user name
entry, save the current clipboard contents to a
variable. Then behave as usual, but after erasing
the username/password from clipboard, re-write the
old clipboard contents to clipboard!
This can only have usability advantages, but there
can be no disadvantage in that behaviour!