Cannot query tables after add columns for AVRO table

DROP TABLE sandw1;
CREATE TABLE `sandw1`(`name` string, `description` string, `cost` decimal(4,2)) STORED AS avro;
INSERT INTO sandw1 values('tuna', 'bread tuna and mayo', 4.99);
INSERT INTO sandw1 values('egg', 'bread egg and mayo', NULL);
DROP TABLE sandwiches;
CREATE TABLE `sandwiches`( `name` string, `description` string ) stored as avro;
INSERT INTO sandwiches select name, description FROM sandw1;

SELECT * from sandwiches;
ALTER TABLE sandwiches ADD COLUMNS (`cost` decimal(4,2));
SELECT * from sandwiches;

hive> SELECT * from sandwiches;
OK
tuna    bread tuna and mayo
egg     bread egg and mayo
Time taken: 0.13 seconds, Fetched: 2 row(s)
hive> ALTER TABLE sandwiches ADD COLUMNS (`cost` decimal(4,2));
OK
Time taken: 0.115 seconds
hive> SELECT * from sandwiches;
OK
tuna    bread tuna and mayo     NULL
egg     bread egg and mayo      NULL
Time taken: 0.072 seconds, Fetched: 2 row(s)

[nightly55-2.vpc.cloudera.com:21000] > SELECT * from sandwiches;
Query: select * from sandwiches
+------+---------------------+
| name | description         |
+------+---------------------+
| tuna | bread tuna and mayo |
| egg  | bread egg and mayo  |
+------+---------------------+
Fetched 2 row(s) in 0.63s
[nightly55-2.vpc.cloudera.com:21000] > ALTER TABLE sandwiches ADD COLUMNS (`cost` decimal(4,2));
Query: alter TABLE sandwiches ADD COLUMNS (`cost` decimal(4,2))
[nightly55-2.vpc.cloudera.com:21000] > SELECT * from sandwiches;
Query: select * from sandwiches

WARNINGS: Field cost is missing from file and does not have a default value.

Fetched 0 row(s) in 0.30s

[nightly55-2.vpc.cloudera.com:21000] > SELECT * from sandw1;
Query: select * from sandw1
+------+---------------------+------+
| name | description         | cost |
+------+---------------------+------+
| egg  | bread egg and mayo  | NULL |
| tuna | bread tuna and mayo | 4.99 |
+------+---------------------+------+