here is a comment from Mr. Markus Mäkelä, Software Engineer , from MariaDB Corporation.

https://groups.google.com/forum/#!topic/maxscale/4TxBg0ukA00

issue :
schemarouter doesn't support prepared statement (stmt) queries, it will route the query to all servers .

maxscale execute every query on both servers (serv_A & serv_B) , it should redirect the query to one where selected database is .
i use schemarouter, it should work as proxy (high availability) .
i see this error only if i used $mysqli->prepare() . it work fine if when i use mysqli_query();
this is what i see on every query (with $mysqli->prepare() ) :
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2017-01-31 09:35:37 error : Failed to execute select listid,eml from max_test_A.table_1 where userid in serv_B:3306. 42S02 Table 'max_test_A.table_1' doesn't exist
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maxscale.cnf & script of stmt of test are in attachments .