Sliding windows - Rule is being fired even when LHS is false

I have a rule that accumulate fact into sliding window. When the count get to a certain threshold the rule should be activated. After the window time is over, I expect that the rule will not fired anymore. The counter of the fact is report as 0, but still the rule is being executed.

drl :

package com.sample;
import com.sample.WindowLength.FactTest;

declare FactTest
@role( event )
end

rule "A500 : test"
when
// count devices per tag id
$counter : Number( intValue >= 2 ) from accumulate (
$d : FactTest() over window:time(1m), count($d))

then
System.out.println("A500: Rule is fired, count = " + $counter + " *********");
end

scenario:

ksession.insert(new FactTest());
ksession.fireAllRules();
ksession.insert(new FactTest());
ksession.fireAllRules();
ksession.insert(new FactTest());
ksession.fireAllRules();

SessionPseudoClock clock = ksession.getSessionClock();
clock.advanceTime(1, TimeUnit.MINUTES );

ksession.fireAllRules();

Result:
A500: Rule is fired, count = 2 *********
A500: Rule is fired, count = 3 *********
A500: Rule is fired, count = 0 *********