Well, I've installed RTT traces into the various USB device states and tracking control pipe state etc. and there definitely seems to be something amiss:
```
[INFO] device.rs:163 - PollResult: Data { ep_out: 0, ep_in_complete: 0, ep_setup: 1 }
[INFO] device.rs:215 - ControlPipe State: CompleteIn(Request { direction: In, request_type: Standard, recipient: Device, request: 6, value: 256, index: 0, length: 64 })
[INFO] device.rs:216 - Incoming request: Some(Request { direction: In, request_type: Standard, recipient: Device, request: 6, value: 256, index: 0, length: 64 })
[INFO] device.rs:163 - PollResult: Data { ep_out: 0, ep_in_complete: 1, ep_setup: 0 }
[INFO] device.rs:215 - ControlPipe State: DataIn
[INFO] device.rs:216 - Incoming request: None
[INFO] device.rs:163 - PollResult: Data { ep_out: 1, ep_in_complete: 1, ep_setup: 0 }
[INFO] device.rs:215 - ControlPipe State: Error
[INFO] device.rs:216 - Incoming request: None
[INFO] device.rs:163 - PollResult: Suspend
[INFO] device.rs:163 - PollResult: Data { ep_out: 0, ep_in_complete: 1, ep_setup: 0 }
[INFO] device.rs:215 - ControlPipe State: Error
[INFO] device.rs:216 - Incoming request: None
[INFO] device.rs:163 - PollResult: Data { ep_out: 0, ep_in_complete: 0, ep_setup: 1 }
[INFO] device.rs:215 - ControlPipe State: CompleteOut
[INFO] device.rs:216 - Incoming request: Some(Request { direction: Out, request_type: Standard, recipient: Device, request: 5, value: 23, index: 0, length: 0 })
[INFO] device.rs:163 - PollResult: None
```

Noticing two things:
* the response to the `SET_ADDRESS` request never gets registered as transmitted
* An EP0-OUT packet is encountered while processing a GET_STATUS response, which is unexpected and causes the control pipe to enter an error state