In the morphology that James Brooks and I did we put the following footnote
on page 63 to the acc. of the noun CARIS;
"Dental stem nouns not accented on the penult, i.e. barytone (¦ 78), tend
to have N rather than A in the accusative singularr. . . .
For example CARIN appears 42 times, CARITA only twice. ELPIS, being
accented on the ultima, has only A, but examples of N in the accusative of
D-stem nouns are ERIS/ERIN, KLEIS/KLEIN (despite being accented on the
ultima; also KLEIDA), and PROFHTIS/PROFHTIN. The HS/HTOS nouns, however,
always have A."
Hope this helps. You can see that I consider this a matter of orthography.
Carlton L. Winbery
Prof. NT & Greek La College