Firing an event trigger for ADD COLUMN?

I'm writing a script that "reverses" ddl operations in an "up" script by
capturing event triggers and generating a "down" script for reverting.
I've got it working great for tables, indexes, etc, but it seems ADD COLUMN
doesn't sent an event, here's the code i'm using, pasted straight from the
documentation:

https://gist.github.com/michelp/c6daa1c123c4743be4f8b08fad5d5396

And here's the results I get, I get an event for dropping a column, but not
adding one:

postgres=# create table foo (bar int);
NOTICE: CREATE TABLE created object: table public public.foo
CREATE TABLE
postgres=# alter table foo add column baz int;
NOTICE: ALTER TABLE created object: table public public.foo
ALTER TABLE
postgres=# alter table foo drop column bar;
NOTICE: ALTER TABLE dropped object: table column public.<NULL>
public.foo.bar
NOTICE: ALTER TABLE created object: table public public.foo
ALTER TABLE
postgres=#

Is this asymmetry a bug? I realize these event trigger functions are
typically written in C, but I'd like to keep this idea contained to a
plpgsql function and cover as many reversible changes as I can.

Thank you,

-Michel