Portalblocks 90 and 119 should disappear when placing manually
(After reading two comments I realized my description was not clear enough. So I changed it to make it more clear)
Background
In creative and survival mode you can use portalblock 90 (Nether) and 119 (End) and place it manually. If you do so, they show a specific behavior:
1) If you try to construct a nether portal manually by placing TWO nether portalblocks together, they disappear. Apparently it shouldn't be possible to create a portal manually.
2) If you try to construct an end portal manually by placing an end portalblock in the End or the Nether, it disappears. Apparently it shouldn't be possible to do this too.
What I expected to happen was...:
1) ... that placing a SINGLE nether portalblock somewhere, it would disappear too.
2) ... that placing an end portalblock in the OVERWORLD it would disappear too.
What actually happened was...:
1) Placing a SINGLE nether portalblock (block id 90) somewhere, it stays. This is possible in Overworld, Nether and even in The End (where you should NEVER be able to create a nether portal). And surprisingly you can go through this single block portal into the Nether. (Side effect: If you go through without an existing normal Nether Portal, you arrive in an invisible Nether. The Nether is not visible until logging out and in).
2) Placing an end portalblock (block id 119) in the Overworld manually, it stays instead of immediately disappearing.
Summary
Apparently it shouldn't be possible to create a nether portal or an end portal manually. But this is not implemented consequently.
1) Two nether portalblocks disappear - one nether portalblock not. Disappears with block updates.
2) An end portalblock disappears in the End and in the Nether. In the Overworld it doesn't disappear.
Comments 6
I agree with Neospector for the first part, they shouldn't disappear since they are not obtainable through any other means, they must be deliberately obtained through commands. Having them disappear automatically would just be counterproductive since they could be used either functionally or decoratively in custom maps.
For the second part, I couldn't reproduce what was given in the "steps to reproduce." (Maybe you missed a step since going through a Nether portal shouldn't make you end up in the overworld in the first place.) However, when I went through the single Nether portal block in the End, the Nether didn't load until I reloaded the world (or it may have been just very laggy). I went into another single Nether portal block again to see if it would take me to an invisible overworld, it seemed to, but it loaded very quickly.
The behavior is not consistent - that's my problem.
If you place TWO nether portalblocks somewhere, they disappear. But if you place only one, it stays. Why do two blocks disappear? Because it should not be possible to build a nether portal manually without a frame and without activation. BUT: you can also walk through a single portalblock. Consequently a single block should disappear too.
Similar with the end portalblock: place it in the Nether or place it in the End - it will disappear (even a single one!) But place it in the Overworld, it stays.
If this inconsequent behavior of block 90 and 119 is a feature, please explain it to me. If it's not a feature, its a bug 😉
No change in V 1.6.2 - you can still place a single nether portalblock in the end (and everywhere else) and jump to the nether. And you can still place an end portalblock in the overworld wherever you like and in any quantity 😞
The first part (that they should disappear) is a suggestion, and does not belong here, it belongs in the Forums.
However, I cannot confirm the "Invisible dimension" part you mentioned in the second part. It lagged a little bit and appeared invisible, but when I took a screenshot with F2 I was in the Nether just fine.