Update schema fails to recognize correct schema

When the primary key is a text string the update:schema command fails to recognize that the database schema is correct, and with every call to update:schema it tries again and again to make the same, unneeded change.

class BillMethod
{
/**

• @ORM\Id
• @ORM\Column(type="string", length=50, nullable=false)
• @ORM\GeneratedValue(strategy="IDENTITY")
  */
  protected $sid;
  ...
  }

When I run update:schema, I tells me this change is needed.

ALTER TABLE billmethod CHANGE sid sid VARCHAR(50) NOT NULL;

But, it's already there.

mysql> desc billmethod;
--------------------------------------------+

--------------------------------------------+

...

The SQL does nothing, and update:schema tells me that this change still needs to be made.