The general challenge of tech company employees who receive equity-connected compensation is they need to make sure the transactions are reported correctly on Schedule D.
The brokerage firm (Morgan Stanley, Merrill Lynch, Fidelity, etc.) may show someone sold stock for $10,000 and apparently made $9,000 of profit... but that $9,000 has already been included in the person's W-2 and thus taxed... Therefore the employee needs to adjust the basis on the Schedule D.
A general observation from a CPA in an area where there's a lot of this accounting going on: Big experienced companies like Microsoft, Amazon, Google, Facebook do an excellent job making sure that the W-2 and 1099-B info syncs.
Often others don't. And this clarification: These "others" can include large public companies with lots of employees.