So, the company let employees have lots of shares, and got a reduction in its taxable profit (which is what the tax legislation says happens in such cases). I expect the employees had large Income Tax bills, or CGT if they sold the shares. It's kind of the same result as if Facebook had paid out lots of cash bonuses — a low profit for the company and income for the employees.
What's wrong with that?
Facebook pays no UK corporation tax for a second year Social media company reports a pre-tax loss of £11.6m for 2013, despite its US parent making a net profit of £900m