End portal does not activate if obstructed by blocks

If the inner 3x3 area of an end portal is obstructed by non-air blocks, the portal will fail to activate. In 1.8.9 or earlier; interfering blocks were destroyed by the end portal's activation. In the case of a failed activation, the end portal can only be successfully activated by replacing a portal frame (only possible in creative) and the eye inside it.

To fix this, either make it so the end portal can be activated again in the case of failure, or allow the portal to activate regardless of interfering blocks.

The portal in the screenshot is built in the correct orientation.