I was wondering how often this bug occurred. :)

You asked me a question about (me) taking quests in a specific order, but it is not me with the problem. So I say again, why ask me?

The problem is not mine. Your assertion makes absolutely no sense.

Yes, the problem affected someone else. You said it has never happened to you. An interested poster then tried to understand why you never have this problem, when other people do. Is that a simple enough recap? Is it wrong in some way?

No, the poster asked me a question that's unrelated to the actual problem, a problem that's not even mine. The order of accepting quests has no bearing on whether you lose the stronghold or not. I refuse to answer a hypothetical non-question.

I was trying to ascertain if this is a problem I might encounter. In fact, IIRC, I think I may have.
(I have never completed the game, but I have started it many, many times. I think I prefer to create characters more than play the game. :)
So I wasn't trying to ensnare you in some elaborate trap; I was just curious if the problem was due to something that might befall many people.
I asked you, specifically, because you seem to be the most well-read / experienced player of this game / series / Infinity engine franchise collection on this forum (possibly in the WHOLE WORLD!!11!) and therefore your insights are both penetrating and valuable.
I would still be interested to know if the fault is because the player is trying to do something "wrong" in the story. As you very well know, part of the appeal of the game is that it is "open world"; this would be a noteworthy asterisk to bullet, considering there is (if I understand your post aright), specifically, a WRONG way to complete some quest.

That's all. You may re-holster your chemical weapons and stand easy. :)

The problem stems from the fact that the quest timer starts when the messenger spawns near the Copper Coronet, not from when he speaks with you. If you leave the area by the other exit before he speaks with you, you miss out.
This is easily done if you have the boots of speed and don't realize he is following you.

I will answer your specific question, viz. "Have you opted for the planar quest before securing the Ranger's cabin?" with this: any other non-related quest has absolutely no bearing on the Ranger stronghold which is not affected by either script or variable of said quests. Therefore, with regard to your question it is impossible to do "something wrong". To do something wrong, you have to be manipulating (one way or another) the game as relating to that specific quest.

Thank you. By answering my question you have given me insight into the underlying process (and its potential faults), which was my purpose. :)

I think I may have done the boots of speed thing, too; I definitely have missed the Ranger's cabin through tardiness. :D

My first playthrough I remember I was lost three levels down in that vampire-infested countryside tomb, never to be retrieved. (Restart that mess!) Damn level-drained undeath!