When I try to create a comment on my table, pgAdmin script generated behind the scene recreates constraints (primary key and foreign keys). It simply add ALTER TABLE ... DROP CONSTRAINT ... and ALTER TABLE ... ADD CONSTRAINT - this is not needed.
COMMENT ON TABLE ... is added at the end of the script too.
Another odd thing is refreshing object explorer on changes of object defs (via GUI). All schema nodes are collapsed and edited object is not visible any more eg. when you put a comment on column. This is very annoying when db contains many objects.
