SMgrRelation hashtable corrupted

On 8 beta1 I get 'SMgrRelation hashtable corrupted'  *sometimes* when
executing the following, but only when there are other clients connecting to
the same database.

ALTER TABLE declines
    ALTER COLUMN comp_name TYPE varchar(128),
    ALTER COLUMN f_name1 TYPE varchar(48),
    ALTER COLUMN l_name1 TYPE varchar(48),
    ALTER COLUMN country TYPE varchar(48);


Chris