ioguix(at)free(dot)fr writes:
> I found a difference of behaviour between 8.3 and 8.4 on IS NULL with
> multi-level arrays with NULL values.
8.3's behavior is just a bug --- try comparing the results when the
values are variables that happen to be null, rather than simple
constant nulls. 8.4 is consistent with that case, 8.3 isn't.
regards, tom lane