Why this regexp matches?!

select 'depesz depeszx depesz' ~ E'^(.*)( \\1)+$';

what's worse:
$ select regexp_replace( 'depesz depeszx depesz', E'^(.*)( \\1)+$', E'\\1' );
 regexp_replace
────────────────
 depesz
(1 row)

I know that Pg regexps are limited, but even grep's regexps match this
correctly:

=$ printf 'depesz depesz depesz\ndepesz depeszx depesz\n' | grep -E '^(.*)( \1)+$';
depesz depesz depesz

Best regards,

depesz

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