You actually have found a bug. The Server shouldn't have sent the END message, as it is reserved for future versions of the client library (thus, the bug is in the Server).

Note that the END message just notifies that the session is being forcibly (and unexpectedly from the client point of view) closed by the Server.
However, the current version of the java client library does not support this notification and just finds that the connection closes at once.
Therefore, without the bug, the session would have been closed the same; you just wouldn't have got the two onDataError calls, but only the final onFailure call.
We cannot fix the bug in short time and we apologize for the inconvenient. For now, you can just recognize the "Incorrect answer" errors and ignore them.

If needed, a look at the corresponding Server log could help us understand the reason why the Server forcibly closed the session.