There is actually some difference in meaning if you do (typical) or don't lenite an adjective after a feminine noun, as Jaybee said. I remember an example of Bróg chailín and Bróg cailín from Peadar Ua Laoghaire, but I don't remember in which of his works he explained it.

I'm very dubious about accepting any explanation from a grammar book that old... I've seen what sort of nonsense they were spouting about English in that era after all.

I'm very dubious about accepting any explanation from a grammar book that old... I've seen what sort of nonsense they were spouting about English in that era after all.

Mind you...can anyone shed any light on the Obair Baile or Obair Bhaile debate...? 
Obair baile is what the native speakers use. We have a native speaker in our local school and the use of "obair bhaile" by the other teachers is a bit strange to her.

I've never heard anything other than "obair" being feminine: 
an obair shuimiúil 
tús na hoibre suimiúla 
na hoibreacha suimiúla 
tús na n-oibreacha suimiúla

Fear na mBróg --> I have heard that there was a difference between obair bhaile and obair baile. One means "homework" (for school), the other one means "the work you have to do at home, like to sweep dust, etc. I don't remember which one is which one. Maybe obair bhaile = sweeping etc and obair baile = school work. 
...Obair is always feminine; sometimes there are exceptions to the rule of séimhiú on a noun that is after a feminine noun in the nominative case, cf tír mór = the continent (or Ireland, as opposed to the small Irish isles, like Tory, the Aran isles, etc), although tír is feminine.
...I've heard that explanation before too Lughaidh, that "obair baile" is school homework and that "obair bhaile" is housework. I have only heard this from people who have attended a particular college under a particular lecturer...I don't think native speakers are generally aware of the distinction. Obair tí is what I normally hear for housework...interestingly there's no séimhiú on that either.
...I see Ó Do/naill has "obair bhaile" for homework...

An chéad cheann: obair tí
An dara ceann: obair bhaile
Níl a fhios agam cén fáth nach séimhítear "tí", ach is é sin a deirtear.

Ní mise a phléigh é. An é "gloine a bhfuil fíon inti / gloine le haghaidh fíona" vs. "gloine atá déanta as fíon (!)" atá i gceist? Ach níl an "obair bhaile" déanta as "baile". Cabhrú, led thoil!

gloine fíona - gloine atá lán d'fhíon, nó lán gloine d'fhíon ("glass of wine", le dul i muinín an Bhéarla)
gloine fhíona - gloine de chineál áirithe ("wineglass")

Ar ndóigh, ní mór eatarthu go hiondúil. Mar shampla,
ubh circe - ubh ar le cearc í
ubh chirce - ubh de chineál áirithe (an cineál a bhéarfadh cearc)
Fág scéalaíocht Hans Christian Andersen as an áireamh agus is beag cás inar chóir dealú eatarthu! Mar an gcéanna an uimhir gutháin (uimhir a bhaineanns le guthán) agus an uimhir ghutháin (uimhir de chineál áirithe, bíodh an uimhir áirithe féin bainteach le fón nó ná bíodh.)

Ach tá roinnt eiseamláirí suntasacha a bhfuil fíordhifear seimeantach i gceist leo:
gloine fíona/fhíona (nó beorach/bheorach, nó cibé a bheas agat féin...)
cos maide/mhaide
culaith mairnéalaigh/mhairnéalaigh


PATRICK -REGARDING AN OLDER POST HERE -Rud eile de: níl an séimhiú féin le brath ach i gcás ainmfhocail bhaininscní agus consan inséimhithe ina dhiaidh, ar ndóigh, ach is féidir an difear céanna a fheiceáil i ngnéithe eile den ghramadach, mar shampla in ord na haidiachtaí:
cupán tae - "cup of tea" nó "teacup"
ach
cupán beag tae - "small cup of tea"
cupán tae beag - "small teacup"

QUOTE -gloine fíona - gloine atá lán d'fhíon, nó lán gloine d'fhíon ("glass of wine", le dul i muinín an Bhéarla)
gloine fhíona - gloine de chineál áirithe ("wineglass")

Ach níl FGB ar aon intinn leat:

gloine, ... ~ fíona, wine-glass; glass of wine.