Mapping fails with MigrateDestinationEntityAPI

I've been running into several issues when trying to migrate from a csv to an entity that I created using Entity Construction Kit.

First, using an int as the source_key fails with the following error when I try to run the migration: "General error: 1366 Incorrect integer value: '1' for column 'sourceid1' at row 1". By specifying the source key as a varchar (see below), I can get one step closer.

$this->map = new MigrateSQLMap($this->machineName,
        array(
          'id' => array(
            'type' => 'int',
            'unsigned' => TRUE,
            'not null' => TRUE,
          )
        ),
        MigrateDestinationEntityAPI::getKeySchema()
    );

// The following change avoids the first error
    $this->map = new MigrateSQLMap($this->machineName,
        array(
          'orgname' => array(
            'type' => 'varchar',
            'length' => 60,
            'not null' => TRUE,
            'description' => 'Company name',
          )
        ),
        MigrateDestinationEntityAPI::getKeySchema()
    );

However, trying to run the migration at this point leads to the error: "Column not found: 1054 Unknown column 'destid1' in 'field list'". If I then manually add the destid1 column, my migration runs successfully.

At this point, I'm not sure if the issue is coming from migrate_extras or the way it interacts with the entity I created with ECK.

Given that this is a one time import that I can massage to work, I am able to move on at this point. But if I can help diagnose or solve the issue, please let me know.