I have a shulker farm based on the RaysWorks design with alternating walls and portals separated by a block of open space. A shulker has teleported to one of the walls, but when it opens up, touching the portal blocks, it doesn't go through to the nether. Even when it opens fully to shoot a shulker bullet.

 My world backup is too large to attach to this issue. (~100M) If you need it, please provide instructions for sending it to you.