Early in 2016, when oil prices were plunging and when US banks were careful to push up their loan loss reserves to exposed E&P loans, we noted something surprising: Canadian banks had barely taken any loss reserves to their exposure in the oil and gas sector.

As and RBC report calculated at the time, if they used the same average reserve level as that applied by US banks, Canadian banks' current loss allowance excluding RBC would surge from $170MM to over $2.5 billion, resulting in a substantial hit to earnings, and potentially impairing the banks' ability to service dividends and future cash distributions.

For months this discrepancy persisted even as oil remained well below last year's levels, leaving Canadian bank watchers stumped as to just how Canadian banks planned to pull this particular "Exxon" without suffering balance sheet impariment, until this morning when we may have gotten the answer how the local Canadian money centers "planned" to resolve this odd accounting gimmick.

Today Bank of Montreal, perhaps the biggest violator of the loan loss reserve recongition, fell the most in two months after restating it restated its regulatory capital ratios for the first three quarters of the year. As Bloomberg first noticed, the shares slid 1.3% to C$84.72 in morning trade, the most intraday since July 27 and the worst performance in the eight-company S&P/TSX Composite Commercial Banks Index. The stock has gained 8.5 percent since Dec. 31. What was most notable about the restatement is that as one analyst calculated, the move was comparable to erasing C$1.3 billion ($1 billion) of excess capital at Canada’s fourth-largest lender.

But before we get there, here is what happened: Bank of Montreal’s Basel III Common Equity Tier 1 ratio, an international measure of capital strength, was 10% for the third quarter, down from 10.5% for Q3, the company said Tuesday in a statement. The lender also restated its CET1 ratio for the first quarter, to 10 percent from 10.1 percent, and the second quarter, to 9.7 percent instead of 10 percent.

Canaccord Genuity analyst Gabriel Dechaine quickly noticed the unexpected revision, and in a note to clientssaid that “this adjustment is tantamount to wiping out C$1.3 billion of excess capital for the bank," adding that the amount could have been used to buy back as many as 15 million shares or 2 percent of stock outstanding. “We can simply translate the elimination of C$1.3 billion of excess capital into forgone capital deployment upside."

The revision means that Bank of Montreal’s regulatory strength now lags behind its domestic peers: Canadian Imperial Bank of Commerce, the country’s fifth-biggest lender, has the highest regulatory capital ratio, at 10.9 percent at the end of July, followed by Royal Bank of Canada, the nation’s largest lender, and No. 3-ranked Bank of Nova Scotia with 10.5 percent. Toronto-Dominion Bank, the second-biggest Canadian lender, has a regulatory capital ratio of 10.4 percent.

However, if as we speculate the revision may have been prompted by the bank's unwillingness to account for souring bad loans, it is only a matter of time before Canada's other banks follow suit.

As for BMO, the bank did not admit the actual reason for the restatement instead providing the following vague explanation: “We determined a need to amend our capital ratios and are correcting the record," according to spokesman Paul Gammal said. “There is no change to net income or shareholders’ equity and we are well capitalized."