Steps to reproduce:

1. Place End Portal frames in the normal pattern, facing the following directions, and fill them with Eyes. This does not create a portal (as expected). (N = facing North, etc.)

     N   N   N

E                   W

E                   W

E                   W

     S   S   S

2. Add one more End Portal Frame block, so that you have the following pattern (where X is an empty space), and fill the block with an Eye.

   N   N   N   X   X   X   S

E                  W

E                  W

E                  W

   S    S    S

Expected Behaviour:

No Portal should form, as there is no correct portal structure. The complete structure's Frame Blocks face the incorrect direction, and should all be rotated 180 degrees, to make it correct.

Current Behaviour:

A Portal is formed north of the South-facing Portal Frame Block.

Additional information:

As End Frame Blocks are unobtainable items in Survival-mode, this should only affect Creative-mode.