cannot drop active portal

Hackers,

While playing with code to enable subtransactions in the storage
manager, I run across this strangeness:

alvherre=# begin; begin;            -- start a subtransaction
BEGIN
BEGIN
alvherre=# drop table foo;            -- no such table
ERROR:  no existe la tabla "foo"
alvherre=# commit;
ERROR:  cannot drop active portal
alvherre=# 


This happens while PortalDrop() tries to drop an active portal.  In this
state, I can't do anything else short of closing the connection.  But
this doesn't happen if I try to run a non-utility bogus statement
("SELECT foo"); the system then allows me to rollback the transaction.

Why is a portal kept active after a utility statement fails?  I've been
reading tcop/postgres.c but I can't find what's different between
utility and non-utility.

Any clues?

-- 
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"People get annoyed when you try to debug them."  (Larry Wall)