Asenion, this was recently discussed on the Daltaí forum. What you are referring to is when the object of the verbal noun is qualified by an adjective. Ag tógáil ceatha would take the genitive. But once additional adjectives are added into that, it turns the object of the verbal noun into a noun phrase that can stand on its own without been declined. The problem is the Gaeltacht use of the genitive is patchy to start with - and so if we only talk about Standard Irish rules here (but bear in mind the Gaeltacht usages are right too), the recommended pattern is as Carmanach recently put it on Daltaí:
Quote:
ag léamh leabhair - reading a book (Gen)
léamh leabhar - reading books (Gen)
ag léamh leabhair Ghaelainne - reading Irish books (Nom because qualified)
ag léamh leabhar Gaelainne - reading an Irish book (Nom because qualified)
ag léamh na leabhar Gaelainne - reading the Irish books (Gen, even though qualified due to the article)
ag léamh an leabhair Ghaelainne - reading the Irish book (Gen, even though qualified due to the article)
When the noun is qualified by an adjective or adjectival phrase, we get:
ag léamh leabhar maith = a good book (Nom)
ag léamh leabhair mhaithe = good books (Nom)
ag léamh an leabhair mhaith = the good book (Gen, even though qualified due to the article)
ag léamh na leabhar maith = the good books (Gen, even though qualified due to the article)
You will notice that Gaelainne or Gaeilge, while being a genitive of the language name - performs an adjectival function, so the rules over "leabhair Ghaelainne" are the same here as for "leabhair mhaithe". I edited my quote from Carmanach - to comment in each line above why the choice was made.