Likely due to the server split in this version, nether portal blocks now take a frame to disappear when updated. As a result, when two nether portal blocks are placed next to each other horizontally with the item, they can be seen to connect.
Nether portal items have an unstable item model which changes depending on blocks which are targeted or in loaded chunks. It uses this model in inventories, when held in first or third person view or as a dropped item.
Initially the Nether portal item would appear as a full cube like many other blocks, but targeting an existing portal block would cause the item to morph into its shape:
Having an existing nether portal block within loaded chunks also appears to influence the shape of the nether portal item. For example, if no existing blocks are loaded, the item may appear in its full cube state, but loading a chunk containing an north-south oriented nether portal will result in the item automatically becoming north-south.
Block items have changed in this version to be brighter and rotated 90 degrees clockwise from their prior appearances. The "pane" appearence shapes can be seen to have been inverted as a result, with east-west oriented how north-south was previously and vice versa.