Setting a portal to "output" does not seem to change the direction of flow for the belt itself within the part.

Setting a input works correctly, and the action of setting a output works correctly... but the belt itself is still moving "in" so the material never leaves the portal despite being able to see it has passed it through the portal and is linked correctly.

The direction tells the portal which way to move the items. But doesn't change the direction of the underground belt. Just press r to rotate the direction of the belt. Im testing a new release that will auto assign the direction of the pop-up based on the belt direction.