For every rule, there is (usually) an exception.
Even in English, the rule is that "x" is pronounced "ks" has exceptions : exact, exile...where the "x" is pronounced "gz."
In Chamorro, the UM infix is usually place after the initial consonant(s).
Kånta = Kumånta
Hånao = Humånao
But there are exceptions. These exceptions do not follow the rule and are tolerated.
They often involve words beginning with the letter N.
Nå'e (to give) should become Numå'e. But in reality, 99% of the people will say Munå'e.
Nå'ye (to add, put in) should become Numå'ye. But one normally says Munå'ye.
That being said, SOME people do say "numå'e" and "numå'ye." Either form is tolerated; either the rule or the exception.
Words starting with Ñ are also often the exception.
Ñålang (hungry) should become Ñumålang (to become hungry), but most people say Muñålang.