"Do we have debates within the Labour Party? Damned right we do but it doesn't lead to the sort of thing that everybody seems to be reporting on at the moment," he said.
"There's been debate across the board. We talk about my leadership, we talk about policy, we talk about speeches. We talk about everything. If we didn't you'd be surprised."
Mr Shearer was elected leader in December by the caucus after a primary-style contest throughout the country against New Lynn MP David Cunliffe.
Mr Nash, a former list MP, has returned to Napier where he wants to contest the 2014 election.
His resignation as chief of staff led to speculation about differences in the office by right-wing blogs such as Whale Oil and Kiwiblog and left wing blogs such as The Standard.
Left wing commentator Chris Trotter yesterday suggested in his Bowalley Road blog that he had changed his mind about Mr Shearer and that "the caucus had picked the wrong guy".
"It's time for the Labour caucus to put an end to the 'unfortunate experiment'," he wrote.
Mr Shearer said he was surprised that speculation from blogs was also appearing in mainstream media.
He appeared most irritated at suggestions [on The Standard] that Mr Cameron had been installed in advance of a leadership takeover by Mr Robertson.
"I speak to Grant three or four times a day on the phone. We're in and out of each other's offices when we are in Parliament together, all day."