As I posted previously, dictionaries don't include new words that are too little used to warrant inclusion. There is a good possibility that 'refudiate', number one in the Oxford Press top ten list for 2010, will be accepted by major dictionaries; none accept it now because the word has yet to 'prove' itself.
"Litigating circumstances"? That made me smile, because 'my son the lawyer' talks about them. But I agree, the words ain't interchangable.

Irregardless has been a subject of controversy for almost 100 years. A much used word, it is included in The Oxford English Dictionary, but its double negative nature is noted and the definition "regardless' is given.
Like refudiate, it is a 'portmanteau' word, probably a combination of irrespective and regardless.