After the roots 1. sthā 'to stand' 2. gā 'to sing' 3. pā 'to drink' 4. pac 'to cook', the affix ktin is used when a word in the feminine gender denoting a 'mere action' is to be expressed.,
This debars the affix अङ् 3.3.106 which generally supersedes क्तिन् in cases of compound verbs ending in long आ. Thus प्रस्थितिः 'a journey' 7.4.40; उद्गीति 'a singing aloud'; गै + क्ति = गा + ति 6.1.45 = गी + ति 6.4.66; सगीतिः 'a concert'; प्रपीतिः 'a cistern'; सम्पीतिः 'drinking together'; पक्तिः 'cooking'.
The repetition of the word भाव in this aphorism, in spite of its anuvritti being understood from sutra 18 is to exclude every other significance.
How do we get forms like अवस्था and संस्था ? Panini himself, in his sutras, has used forms like व्यवस्था &c. See 1.1.34. This is enough justification for us to derive forms like अवस्था, संस्था &c. by applying the affix अङ् under rule 106 inspite of the present sutra, which requires us to apply क्तिन् only.,