在主语从句中it is+adj+that后不是加虚拟语气should+动词原形

It is strange that he had made a mistake. 奇怪的是他犯了一个错误。
这是一个陈述句，就是陈述一个事实：他犯了错误让人有点奇怪。
It is strange that he (should) have made a mistake. 他居然犯了一个错误，真令人奇怪。
这是虚拟语气，说话者是在责备他本不应该犯错。
It is/was ＋形容词/名词＋that主语从句多数情况下用虚拟语气，表达一种要求，命令或者责备，但是如果只是表示陈述一个事实而不是强烈的感情，完全可以用一般的陈述语气。
以下为词典原句:(不过考试建议你还是多用虚拟语气)
It is a shame that the rain spoiled our picnic.
真可惜，这场雨把我们的野餐给搅了。
It is a pity (that) he lost so much money.
他损失这麽多钱，真是遗憾。
He was a very brave man and it is surprising that he lived so long.
他是一个非常勇敢的人，而令人惊讶的是他活得那麽长命。
It is strange that nobody knows where he lives .
真奇怪，谁也不知道他住在哪里。

附：虚拟语气用在主语从句中有以下几种情况：
1.在句型 "It is important (necessary, strange, impossible, natural) that .... " 中，that后面的从句中的谓语动词用：(should) + 动词原形。 如：
It's necessary that we should have a walk now. 我们有必要出去散散步。
It's natural that she should do so. 她这样做是很自然的。
It's important that we should take good care