To make this, Create a portal(size/shape doesn't matter), then place a block inside near to portal teleportion using /setblock command, then break block(break inside portal that contains blocks and portal frame) and walia! the glitched portal! This is used as custom portals.

look, the core block got replaced with other blocks, without core block, the portal wont close up.

Beware that this is a bug and will be fixed eventually (probably in BP 0.4 or 1.0, whichever comes first). I'm keeping it alive though until there's an alternative.

Duplicate of #231