Oddness 7.3 vs 7.4

I notice this in 7.3.4:

test=# create table test (a int4, b int4);
CREATE TABLE
test=# create index idx on test(a) where b is null;
CREATE INDEX
test=# \d test     Table "public.test" Column |  Type   | Modifiers
--------+---------+----------- a      | integer | b      | integer |
Indexes: idx btree (a) WHERE (b IS NULL)

test=# alter table test drop column b;
ALTER TABLE
test=# \d test     Table "public.test" Column |  Type   | Modifiers
--------+---------+----------- a      | integer |
Indexes: idx btree (a) WHERE ("........pg.dropped.2........" IS NULL)


And this in 7.5CVS:

test=# create table test (a int4, b int4);
CREATE TABLE
test=# create index idx on test(a) where b is null;
CREATE INDEX
test=# alter table test drop column b;
ALTER TABLE
test=# \d test     Table "public.test" Column |  Type   | Modifiers
--------+---------+----------- a      | integer |


I cannot think of any commit that fixed that???  Is it fixed in 7.3.5?

Chris