The feminine of these adjectives in PUL's Irish is worth noting, as it has largely aligned with the masculine.
Let's start with the masculine singular:
Nom. fear bacach
Voc. a fhir bhacaigh
Gen. fir bhacaigh
Dat. d'fhear bhacach
And for completeness give the plural:
Nom. fir bhacacha
Voc. a fheara bacacha
Gen. fear mbacach
Dat. d'fhearaibh bacacha
Now the feminine singular, let's give what would have been the historically correct forms and then give PUL's forms:
Nom. bean bhacach bean bhacach
Voc. a bhean bhacach a bhean bhacaigh
Gen. mná bacaí ???
Dat. do mhnaoi bhacaigh do mhnaoi bhacach
O'Rahilly mentions (at
http://www.jstor.org/pss/30007912) that the tendency for the feminine vocative adjective to be formed in -igh like the masculine is of longstnding, and found since the latter half of the 17th century. Examples in Séadna include things like "a thoice bhig" (you little hussy) instead of "a thoice bheag". This example shows that this tendency is found in all feminine adjectives and not just those in -ch.
An example from Séadna of the feminine dative adjective of an adjective in -ch aligning with the masculine is: "Agus geallaim dhuit ná raibh an misneach céadna sa chois bhacach ag gabháil suas a bhí inti ag gabháil síos aige".
An example from Niamh of the feminine genitive adjective of an adjective in -ch aligning with the masculine is "i gcoinnibh na sluagh págánach". However, it is unclear to me if this is genitive singular or genitive pural, as slua is feminine in PUL's books; if genitive plural the adjective would be eclipsed, but the eclipsis could also have been left off. Another possibility is that págánach is a noun and not an adjective here, in the genitive plural. Given my doubts over the interpretation of this sentence, I have put ??? for the genitive singular forms in PUL's works pending further evidence.
