Lenition-maybe

 Hmm, one might envision that the protolanguage had something like '@caiyar'
 as infinitive and 'caiya' is 1s, (having the @ as infinitive marker) and
 where the initial sounds regularly dropped, leaving 'caiyar' infinitive and
 'aiya' 1s.

 I was thinking about this actually, from the moment I wrote it, could
 it be some form of lenition?  Maybe its like the Irish past tense:

      thóg sé "he raised"  as opposed to tógann sé "he raises"

There might be some sort of lost lenited particle in the 1st person,
though why it doesn't occur in the 2nd and 3rd (I don't remember the
forms I just know it doesn't) is still a mystery.

    Elliott