Sliding time window ignored when using @timestamp and pseudo clock

When using a custom @timestamp together with PSEUDO clock, all events are accumulated rather than just those within the window:time period. I have tried using long (millisecond) and java.util.Date without success.

==================================

declare SimpleObject
@role(event)
@timestamp(customTime)
@expires(10m)
end;

rule "honour custom timestamp"
when
$avgVal : Number (longValue > 0) from accumulate ( SimpleObject($valueLng : valueLong ) over window:time (10s) from entry-point "SimpleEP", average ( $valueLng ) )
then
System.out.println("avg: " + $avgVal);
end

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import java.util.Date;

public class SimpleObject {

private long customTime;
public long valueLong;

public SimpleObject(Date customTime, long valueLong)

{ this.customTime = customTime.getTime(); this.valueLong = valueLong; }

public long getCustomTime()

{ return customTime; }

public void setCustomTime(long customTime)

{ this.customTime = customTime; }

public long getValueLong()

{ return valueLong; }

public void setValueLong(long valueLong)

{ this.valueLong = valueLong; }

}
------------ Trivial Spock/Groovy unit test ----------------
@IgnoreRest
def "should honour custom timestamp"() {
when:
use (TimeCategory)

{ def now = new Date() simpleEp.insert(new SimpleObject(now, 100)) ksession.fireAllRules() clock.advanceTime( 5, TimeUnit.SECONDS ); ksession.fireAllRules() simpleEp.insert(new SimpleObject(5.seconds.from.now, 90)) ksession.fireAllRules() clock.advanceTime( 5, TimeUnit.SECONDS ); ksession.fireAllRules() simpleEp.insert(new SimpleObject(10.seconds.from.now, 80)) ksession.fireAllRules() clock.advanceTime( 5, TimeUnit.SECONDS ); ksession.fireAllRules() simpleEp.insert(new SimpleObject(15.seconds.from.now, 70)) ksession.fireAllRules() clock.advanceTime( 5, TimeUnit.SECONDS ); ksession.fireAllRules() simpleEp.insert(new SimpleObject(20.seconds.from.now, 60)) ksession.fireAllRules() clock.advanceTime( 5, TimeUnit.SECONDS ); ksession.fireAllRules() simpleEp.insert(new SimpleObject(25.seconds.from.now, 50)) ksession.fireAllRules() clock.advanceTime( 5, TimeUnit.SECONDS ); ksession.fireAllRules() }

then:
1 == 1 // no assertions - we're examining the stdout.
}
==================================
OUTPUT (INCORRECT - all values are included for each evalutation):
avg: 100.0
avg: 95.0
avg: 90.0
avg: 85.0
avg: 80.0
avg: 75.0

Note that when commenting out the @timestamp tag the output changes to the following (correct) output:
avg: 100.0
avg: 95.0
avg: 90.0
avg: 85.0
avg: 80.0
avg: 75.0
avg: 70.0
avg: 65.0
avg: 60.0
avg: 55.0
avg: 50.0

Also note that when using the REALTIME clock with Thread.sleep the output is correct.