drools 规则引擎 over window:time(1d)的问题

drl文件中定义

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package com.sample

declare Activity
@role( event )
@timestamp(txTime)
end

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rule "totaltimessrule"
salience 1
when
$account:Account($accountnumber:accountnumber) from entry-point ActivityStream
$totaltimes:Number(intValue >= 20)from accumulate(
$Activity:Activity() over window:time(1d) from entry-point ActivityStream, count($Activity))
then
System.out.println($accountnumber);
System.out.println(drools.getRule().getName());
end

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然后在java代码中插入的Activity的txtime（规则引擎的时间戳）全为 2011-6-1

时钟采用realtime实时时钟，执行时间为2011-6-7

采用滑动窗口over window:time(1d)按说应该取自实时时钟2011-6-7当天数据作为活动窗口数据，也就是说没有数据，按说将不会触发该规则，为啥触发了呢，而且每次执行结果具有不确定性

when
$now: CurrentTime() from entry-point "My Stream"
//The following should fetch all events occurred in the last 2 seconds)
$event: MyEvent(this before[2s, 2s] $now) from entry-point "My Stream"
then
System.out.println($event.getEventName() + ": Event Occured!!!" + $event.getEventDateTime().toString());
end

作为权宜之计