Notice the Brood Hunter at the top of the image with the mouseover from attempting to cast 'Web' from my Black Widow. The tile is 'blocked' (cannot be moved into) but the Brood Hunter appeared in it, and cannot be targetted by Web (the cursor is unfortunately invisible in the screenshot, but it shows the o with a slash to indicate I cannot cast the skill, and the mouseover reads 'Cannot hit friendly targets with this ability.') Obviously, the Brood Hunter is not a 'friendly' unit.
