In conjunction with the words sādhu 'good' and nipuṇa 'skilful' when they denote respect, the 7th case-affix is used, provided that the word prati is not used.,
मातरि साधुः or निपुणः 'good behaved towards his mother'? But साधुर्देवदत्तो मातरं प्रति 'Devadatta is good behaved towards his mother.'
Why do we say 'when respect is denoted'? Observe, साधुर्भृत्योराज्ञः 'the servant is good towards the king.' Here it is a bare statement of a fact.
The exception applies not only to प्रति but to other prepositions, like परि, अनु &c., as, मातरं परि साधुर्देवदत्तः ॥,