Hello,
I have 2 server, MySQL 5.0.45 (Ubuntu 7.10). Second, MySQL 5.0.51a (Ubuntu 8.04).

I dump my database routine with this same command
mysqldump --host=host --port=port --user=user --password=pw --compress --quick --compact --skip-comments --no-create-info --no-data --routines --result-file=temp.sql mydatabase

First Server (5.0.45) works well, every procedures, functions, triggers are dumped.
Second Server (5.0.51a) only dumps procedures and functions, not triggers.

I've check the user privileges between those 2 server, everything seems same.
I also tried using mysqldump packaged with MySQL 5.0.67 with both server, the result is same, still can't retrieve triggers from 5.051a server.

Any idea?