[gretch]

What the law says and enforcement of the law are sometimes 2 different things, but generally employees should not be shorting their own stock, lock up or no lock up.

The issue is that this creates a conflict of interest.

In the worst case scenario, as an employee, you can literally do a bad thing to cause the stock to go down. E.g. An engineer can make a bug which blows up a rocket.

So then you could short the stock, bug a rocket, and become super rich.

It's the same issue with athletes betting on their own team - it's trivial to throw the game.