8.4.0 data loss / HOT-related bug

Hello,

8.4.0 installation on i686 modern Linux, a simple production app with ~4
users entering data; normalised, no weird stuff happening there. Recently:

ERROR: missing chunk number 0 for toast value 120741 in pg_toast_29644

This table has table_log and a "before update" trigger setting
"NEW.last_modified = now()". The broken toast is a HTML blob, stored in
a "text" column.

This particular row currently has last_modified="2009-08-11", but table_log
says it has been updated on "2009-08-12" -- so, data loss.

Please see the attachment for the xmin,xmax,cmin,cmax,ctid values of
these rows. Andrew Gireth has asked for the hexdump of page 539 of the
"promocje" table: http://radek.cc/promocje.hexdump

About a week after I've upgraded to 8.4, the users of this application
have started to complain, that some rows are disappearing.

--
Radosław Zieliński <radek(at)pld-linux(dot)org>