Interesting error and not a useful intervention by Klipper <lol> Check
the setting in Klipper to see if any actions have been added but in
the end you may need to purge and then re-install using a package
manager such as Muon or Synaptic. Note the Muon Software Center will
not be able to do this, use Muon Package Manager to select Klipper and
then select 'Mark for purge' to remove all settings etc before putting
it back in again.

Then again - have you installed any other clipboard tool ? If so then
that may be the problem so purge that one instead and see if that
fixes this annoying glitch.

No, I have not deliberately added any extra
clipboard tool.

Have now purged and re-installed Klipper. The next day or so should
show the success/failure of this change.

As suggested, I have purged and re-installed
Klipper. Last evening while composing and editing an
email in Thunderbird, a previous deletion was automatically
re- inserted several times.

I guess that the computer is haunted.

X-Files aside, there has to be a reason somewhere <lol> Since it's
happening in multiple programs the root cause has to be something that
is sending the 'paste' command. Have you a wireless keyboard and/or
mouse as radio interference could be giving false signals that the
computer is picking up as paste instructions.

Might be worth trying a different keyboard or mouse anyway to rule
that one out.

Once had a weird problem with a PC where the mouse pointer would fly
all over the screen and randomly click on icons as it did. This was
eventually tracked down to electrical noise from a failing PSU so
these seemingly random events can have all sorts of causes !!

I had been wondering about something odd in the
motherboard.
Had not considered wireless interference. I do have two other systems on
separate partitions and recall I did have a similar pasting issue with
Mepis.

Both keyboard and mouse are wired. My amateur radio gear shares the desk,
but nothing was switched on at the time. That equipment runs off a 12 volt
battery system with a transformer trickle charger so noise from a
switch-mode
power supply is not an issue. Thinking further on that thread, there is
only one
transformerless power unit within a few metres, that's for the portable
phone.

More investigation needed. Thanks for pointing me at the possibility of
R.F. interference. Will report progress.

Can you try a different keyboard?

Yes, I am trialling changing both mouse & keyboard.
Will advise the results when they are definite.

Could you try a different screen grab tool as a test? I read that Mozilla put
Thunderbird on the back-burner for improvements, too.

It's not just Thunderbird, this automatic pasting happens regardless
of what I am using, Libre Office, Calligra, Firefox etc.

in mid summer NZ where down country there
was some 16 inches of rain in a day. Anyone for camping??

I have had problems with xubuntu in Abiword and LO-writer. I don't
think we are the only ones.