DROP SCHEMA xxx CASCADE: ERROR: could not open relation with OID yyy

Hi all,
I'm trying to debug an ugly error triggered from a "DROP SCHEMA xxx CASCADE"
call inside a function.

The call is the last step of the stored pl/pgsql procedure.

I've verified that removing the "DROP SCHEMA" command from _inside_
the function body and performing it _outside_ it (right after return)
everything works fine.

Note that the schema that the function is trying to drop was created
by a function called by the function attempting to drop it.
Both function (the one which creates the schema and the one which
attempts to drop it) are defined as VOLATILE.

Also, I can see traces of the DROP SCHEMA CASCADE being executed, till
the ERROR comes out (lots of traces for cascading objects).

This is :
 PostgreSQL 8.4.3 on x86_64-pc-linux-gnu, compiled by GCC gcc-4.4.real (Ubuntu 4.4.3-4ubuntu5) 4.4.3, 64-bit

Do you have an idea on how to further debug this ?
TIA.

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