The number of new, unsold condos in Toronto swelled from less than 1,000 in December, 2014, to nearly 3,000 in May, 2015, the Canadian Mortgage and Housing Corporation and CIBC say.

According to a CIBC research note released Monday, the number of unabsorbed condos in the city in May was the highest it's been since the 1990s. The number dropped significantly the following month, when it fell by more than 800 units.

And, the note says, investors have taken note of the dramatic rise and fall.

"This meteoric ascent was not only highlighted by the Bank of Canada as a sign of vulnerability, but also by various short-Canada investors—using that surge as the ultimate illustration of the bubbly Toronto condo market," CIBC Deputy Chief Economist Benjamin Tal wrote in the research note.

Usually, Tal writes, when developers find it hard to sell completed condos, it's a "sign of troubles ahead."

But in the case of the GTA, he says the fluctuating numbers aren't necessarily a reason to panic.

In his note, Tal breaks down the numbers by region, and compares the amount of unabsorbed condos with the number of completed new units.

Using data from the CMHC, Tal finds that 26,000 condos were completed in the first half of 2015 – approximately three times more than the number of condos completed in previous years.

He also notes that approximately half of the unabsorbed condos are in the City of Toronto, rather than the surrounding suburbs.

Digging deeper, he notes that almost one-third, or 31.9 per cent, of the unabsorbed units belong to just four developers. And about 24.4 per cent of unabsorbed units are concentrated among just five condo projects.

While Tal says higher interest rates and an increase in condo "resale activity" could cause excess supply in the future, for now, the number of unabsorbed units doesn't mean the bubble is about to burst.

"Those who look at the rise in unabsorbed units as a sign of increased vulnerability are barking up the wrong tree," Tal's research note says.

Meanwhile, on Canada's West Coast, condo sales tell a different story.

In Vancouver, the number of unabsorbed units fell from more than 2,000 to 1,100 in the past year.

Overall, the latest CMHC Canadian housing market outlook, which was also released on Monday, predicts that Canada's housing market will moderate in the rest of 2015, 2016, and 2017.

According to the report, a rise in market activity in Ontario and British Columbia has offset the slowdown in Alberta, where falling oil prices have hit hard.

Additionally, the CMHC report expects new home construction to slow down, as some builders encourage buyers to go for completed but unsold units.

Because of this, the corporation says it expects Canadian housing prices to even out in the next few years.

"House price growth is expected to slow down as MLS sales will favour moderately priced homes," the report says.