We have a response here that talks to some of the specifics behind its SBC expenses year-over-year, and what factors can influence it.
Much of these expenses are reported on the financial statements each quarter at fair value, and so although they might have a vesting period of three to five years, the fair value expense of these are recorded. When the DSUs vest, there should not be a material change to the income statement since the options were already accounted for using their fair value over the previous financial statements.
Even though the stock price has risen dramatically over the years, this increase has been accounted for on the financial statements already. A decrease in share price quarter-to-quarter can actually benefit the financials as the fair value of these expenses can decline.