There are certain exceptions to this: some substances, though madhura, kashya and tikta in rasa, are ushna in veerya such as brihat pancha mula and meat of aquatic and marshy animals.
Rock salt, though being lavana, and amalaka, though being amla in rasa, is not ushna (in veerya). Arka, aguru and guduchi are tikta (in rasa) but ushna (in veerya).
किञ्चिदम्लं हि सङ्ग्राहि किञ्चिदम्लं भिनत्ति च| यथा कपित्थं सङ्ग्राहि भेदि चामलकं तथा ||५०||
Likewise, there are also variations in actions of rasa. Some substance of amla rasa is astringent (such as kapittha) while other is purgative (such as amalaka).