coalesce in execute crashes backend

Vinod Kurup (vkurup(at)massmed(dot)org) reports a bug with a severity of 3
The lower the number the more severe it is.

Short Description
coalesce in execute crashes backend

Long Description
When I use a coalesce statement to calculate an expression that is part of a dynamic query, it crashes the backend. Interestingly, it works if I use constants as arguments to coalesce.

Sample Code
select version();

create function vk_test()
returns integer as '
declare
v_id integer;
begin
v_id := 2;

raise notice ''try a constant.'';
execute ''select '' || coalesce(2,0) || '';'';

raise notice ''that worked'';

raise notice ''now, try a var with the same value.'';
execute ''select '' || coalesce(v_id,0) || '';'';

raise notice ''we never get here'';
return 0;
end;' language 'plpgsql';

select vk_test();

version
-------------------------------------------------------------
PostgreSQL 7.1 on i586-pc-linux-gnu, compiled by GCC 2.95.3
(1 row)

CREATE
psql:junk.sql:24: NOTICE: try a constant.
psql:junk.sql:24: NOTICE: that worked
psql:junk.sql:24: NOTICE: now, try a var with the same value.
psql:junk.sql:24: pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally
before or while processing the request.
psql:junk.sql:24: connection to server was lost

server.log:
NOTICE: try a constant.
NOTICE: that worked
NOTICE: now, try a var with the same value.
Server process (pid 7516) exited with status 11 at Tue Jun 12 14:32:13 2001
Terminating any active server processes...
NOTICE: Message from PostgreSQL backend:
The Postmaster has informed me that some other backend died abnormally and possibly corrupted shared memory.
I have rolled back the current transaction and am going to terminate your database system connection and exit.
Please reconnect to the database system and repeat your query.

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