I am trying to use Drools Fusion (5.6.0 or 6.0.1) to correlate events, but can't get the internal mechanism for expiring events to work in my rule.

I made up a simple example that detects duplicate messages over a short time window. The rule below seems to work fine, but facts accumulate indefinitely in the working memory. Changing window:length(1) to window:time(10s) does not solve the issue.

declare DataEvent
    @role(event)
end
rule "Detect duplicates"
when
   DataEvent ( $text: text ) over window:length(1)
   ArrayList( size >= 2 ) from collect( DataEvent( text == $text )  over window:time( 10s ) )
then
    System.err.println("Duplicate detected");
end