Trigger.sgml

I am working as a volunteer to translate docs to Japanese. I have been
having hard time to parse the following sentence in
doc/src/sgml/trigger.sgml.

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The possibility of surprising outcomes should be considered when there
are both <literal>BEFORE</> <command>INSERT</command> and
<literal>BEFORE</> <command>UPDATE</command> row-level triggers that
both affect a row being inserted/updated (this can still be
problematic if the modifications are more or less equivalent if
they're not also idempotent).
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Especially I don't understand this part:

(this can still be problematic if the modifications are more or less
equivalent if they're not also idempotent).

It would be great if someone could enligntend me.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp