BUG #5507: missing chunk number 0 for toast value XXXXX in pg_toast_XXXXX

The following bug has been logged online:

Bug reference: 5507
Logged by: Shinji Nakajima
Email address: sinakaj(at)jops(dot)co(dot)jp
PostgreSQL version: 8.3.8
Operating system: Red Hat Enterprise Linux Server release 5.3 (Tikanga)
Description: missing chunk number 0 for toast value XXXXX in
pg_toast_XXXXX
Details:

Error message called "missing chunk number" occurred when I did select of
the specific column of the specific table.
I did not update this record, but was in such a condition suddenly.
There seems to be the person that a similar phenomenon
occurs."http://www.ruizs.org/archives/138"
I delete a record, and the system restores, but prime cause is unknown.
Will this be a bug of the databases?