simple_heap_update: tuple concurrently updated -- during INSERT

Dear Gurus,

I tried to shuffle through the archives but was lost in the technical
details. Please feel free to tell me a search keyword suitable for my case
if there's any.

QUESTION1: is this error _always_ harmless (other than transaction
rollback)?
QUESTION2: is this reported exactly like other errors? i.e. in psql, through
psqlodbc, etc.

As you can see below, this came during an INSERT. I don't really understand
the warning.

QUESTION3: May I assume that the transaction aborted even before it began?
QUESTION4: If that's so, does it rule out triggers and such?
QUESTION5: May it be a problem in 7.3.x that's fixed in 7.4.y?

System: PostgreSQL 7.3.4, Dual Xeon HT

Log:
ERROR: simple_heap_update: tuple concurrently updatedog.
LOG: statement: INSERT INTO pakolas_cikktetel
(cikk, minoseg, helyrol, mennyi, pakolas, sorszam, helyre) VALUES
(102165, 1, 1488, '25', 68615, 1, 1338)
DEBUG: AbortCurrentTransaction
WARNING: AbortTransaction and not in in-progress state

I read in an earlier post that turning on statement logging and duration may
help. If we can reproduce this error, I will. So far this is the only
occurence.

G.
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