Accumulate with vars having a different order than the one imposed by Declaration's hashCode causes a ClassCastException

Running the following drl causes a ClassCastException:

import java.util.List
declare MessageHolder
id : String
msg: String
end

query getResults( String $mId, List $holders )
accumulate(
$holder : MessageHolder( id == $mId, $ans : msg ),
$holders : collectList( $holder )
)
end

rule "Init"
when
then
insert( new MessageHolder( "1", "x" ) );
end