failed to re-find parent key in "..."

Hello all,

a few days ago I bumped into this:

---------------------------------------------
# vacuumdb -f -z -a
vacuumdb: vacuuming database "postgres"
VACUUM
vacuumdb: vacuuming database "rtdata"
vacuumdb: vacuuming of database "rtdata" failed: ERROR: failed to
re-find parent key in "timeslots_strs_var_ts_key"
---------------------------------------------

We are using postgres 8.1.4 and I realise this has been fixed in 8.1.6
but...

...before updating all our servers I need to have an idea of the extent
of the impact of this error.

It seems to me that this error may cause the VACUUM, AUTOVACUUM and
VACUUM FULL operations to fail partially or totally. Am I correct ? Or
does this only have impact on VACUUM FULL ?

We run many servers with a database application very heavily updated. In
this scenario do I tell my boss that "updating postgres would be nice"
or that we "we _must_ update postgres" ?

What risks are we facing if we choose not to update postgresql ?

thanks a lot for your advice.

joao