It might be because you didn't live for one full year last year. If that's the case, your personal amount will be prorated based on the # of days you've been here, therefore the tax free amount will be lower.
星期一终于收到了Notice of Assessment,确实是我在报税时忘了扣掉配偶的未居住天数。但是税务局在计算时也出了差错:我们去年在加拿大居住了245天,但是他们在算配偶的退税时只计算了240天。昨天给税务局打电话,接电话的agency承认少算了5天(差了150块),然后让我在网上添一个要求review的form,他们会打电话通知review的结果。我的电话中间被转了两次,3个agency的态度都很好。