RE:UBS ShortingJust a little observation.
In a share offering (or a bond offeering) brokers are underwriters. That means that they are the middle man between the corporation and the market. They buy the shares to offer them in the retail market. They are stick with the price and the volume agreed. But to minimize this risk, they do a ''road show'' before the final agreement to evaluate the market appetite, accept reservations and determine the price.
They are not the final buyer; their business is the intermediation for fees (2% to 4%) not speculation. More the offering is from a weak company, less risk they will take. So, in the case of 2018 Bombardier offering, it would be surprising that they took a risk. Banks are strickly regulated