After creating an entry in a custom object the returned ID has AA2 appended to the end. Is this normal?

The ID as you see has AA2 added to the end, when I view this entry in the dashboard the URL only shows a00i0000009cDXN which is the ID of the entry. The entry displays even if AA2 is added.

Upserting Contact (existing) Array ( [0] => stdClass Object ( [id] => a00i0000009cDXNAA2 [success] => 1 ) )

Just wondering if this is normal with the API and PHP Toolkit. I'm using a developer account and the SOAP client.

Thanks