postfix 3.1.0-3 fails on mysql table lookup

[Joel Linn]

what I get in the log:
Jul 3 01:21:40 postfix/cleanup[10334]: warning: mysql query failed: Commands out of sync; you can't run this command now
Jul 3 01:21:40 postfix/cleanup[10334]: warning: mysql:/etc/postfix/sql/aliases.cf lookup error for "<email address hidden>"
Jul 3 01:21:40 postfix/cleanup[10334]: warning: EF7AE1C0FCE: virtual_alias_maps map lookup problem for <email address hidden> -- message n$

Configuration:
virtual_alias_maps = mysql:/etc/postfix/sql/aliases.cf

and the query in that file:
query = CALL get_aliases_destinations('%u', '%d')

the stored procedure in the database could be as simple as
CREATE PROCEDURE `get_aliases_destinations`(IN user VARCHAR(64), IN domain VARCHAR(255))
BEGIN
 SELECT CONCAT(destination_username, '@', destination_domain) AS destinations FROM aliases WHERE source_username = user AND source_domain = domain AND enabled = true;
END

The bare select itself as query does work fine.
The crucial thing is that <email address hidden> already is the alias destination, so the first query worked fine. In fact postalias -q .... returns valid results.
I believe this occurs because of the mysql library returning an second empty result set which is not removed/cleared by postfix.
See this discussion which describes a similar issue:
http://stackoverflow.com/questions/6583020/mysql-stored-procedure-caused-commands-out-of-sync
I'm not familiar with the postfix sources but I think a possible fix could be inserted into the plmysql_query function in dict_mysql.c similar to what is discussed in the link and a dozen similar mysql api issues on the web.