I don't think we ever supported this use case with UPS, we never really documented an example using multiple senders, and  the developer can have a different registrar for each sender if she needs this feature with the new (GCM 3.0) APIs.

Because we are already using a major version jump for dropping JDK6, I propose we change the push registrar to only accept a single senderId instead of allowing multiple sender Ids.  This more accurately reflects what the service (GCM) is doing under the hood now anyway.

If someone has an objection let me know and we can discuss it.  Otherwise I'll continue down this path.

XOXO,

Summers