When Warren Buffett acts, investors notice. And after he took a roughly $300 million position last month in Home Capital Group, a troubled Canadian mortgage underwriter, some investors saw it as a vote of confidence not only in that company, but also in Canadian stocks over all.

Al Rosen takes a different view. A veteran forensic accountant and independent equity analyst who predicted the collapse of Nortel Networks, the Canadian telecom company, two years before its 2009 demise, Mr. Rosen has a message for people investing in Canadian stocks: be wary.

It is a mystery to Mr. Rosen why Mr. Buffett bought into Home Capital Group, a company that has been the subject of a titanic battle between the investors who believe in the company and other investors — short sellers — who do not. Certainly, Mr. Buffett expects to make money on his deal. But in an interview, Mr. Rosen said he thought there was more to the story than the markets yet know.

Mr. Rosen is certain of this: International accounting rules followed by Canadian companies since 2011 are putting investors in Canadian stocks — not just Home Capital Group’s — at peril. Canada’s rules, which are substantially different from the generally accepted accounting principles (G.A.A.P.) governing American companies, give much more leeway to corporate managers when it comes to valuing assets and recording cash flows.