Karnatakabhashabhushana 8.4

Not so when the sense is negative.

When the sense of negation is understood, those verbal terminations do not occur beginning thus with the sounds da, dapa, and va; they remain purely in their own form.

māḍaṁ,

māḍar,

māḍay,

māḍir,

māḍen,

māḍevu.