@expires( -1 ) should disable Event expiration

Defining an event with @expires( -1 ) should disable event expiration. However, when configuring my event like this:

declare SimpleEvent
    @role( event )
    @timestamp( logicalTimestamp )
    @expires( -1 )
end

and having a rule like this:

rule "rule_1"
    when
       $s: SimpleEvent ()
       not SimpleEvent (this != $s, this after[0, 30s] $s)
    then
       System.out.println("No event within 30 seconds of this event: " + $s.getId());
end

the event is still expired and retracted from WM after 30 seconds (the expiration time inferred from the temporal constraint in the rule).

Reproducer can be found here: https://github.com/DuncanDoyle/drools-disable-expiration-issue
Run 'mvn clean test' to reproduce.