zero_damaged_pages doesn't work

Is the zero_damaged_pages feature expected to work in 8.3.11 ?

I have a fair bit of evidence that it doesn't (you get nice messages
in saying that the page is being zeroed, but the on-disk data does not 
change).
I also see quite a few folk reporting similar findings in various form
and mailing list posts over the past few years.

I can use dd to zero the on-disk data, but it'd be nice to know
definitively if this feature is expected to work, and if so under
what conditions it might not.

fwiw I am enabling zero_damaged_pages using a set command
in a client session, not in the server's config file. The symptoms
I observe are that a query that previously errored out due to
a bad page header error will succeed when zero_damaged_pages
is enabled, the log says that the page is being zeroed.
However the same query run subsequently without zero_damaged_pages
will again fail, and pg_filedump shows that the on-disk data
hasn't changed.

Thanks.