GUC failure on exception

Tim Bunce just showed me the following oddity:
   andrew=# SET SESSION plperl.use_strict = on;   SET   andrew=# SHOW plperl.use_strict;    plperl.use_strict
-------------------   on   (1 row)
 
   andrew=# DO $$ elog(ERROR,"error") $$ language plperl;   ERROR:  error at line 1.   CONTEXT:  PL/Perl anonymous code
block  andrew=# SHOW plperl.use_strict;    plperl.use_strict   -------------------    off   (1 row)
 


Somehow we have lost the setting, because the first use of plperl, which 
called the plperl init code, failed.

It appears that whatever rolls it back forgets to put the GUC setting 
back as it was, and now it's lost, which is pretty darn ugly. And you 
can now run code which fails the 'strict' tests.

If anyone has a quick idea about how to fix that would be nice. 
Otherwise I'll try to delve into it as time permits.

cheers

andrew