Thank you all for the answers, they covered me well.
>> Is this worth a bug report? I can file one if the issue is not known.
>
> No. It's just a missing optimisation. We know about it.
It's good I shot an email first then. FWIW my usual way in other projects
would be to check the bugtracker, and just "follow" the relevant issue if
it's minor like a missing optimisation. I didn't find a way to search for
"known issues" in the Postgresql project.
Dimitris