It's counter-intuitive because you are saying that partway through your long rest you can regain some (but not all) of your rest-racharge abilities, and that you can spend HD and then regain them all 7 hours later.
The sticking point for me is the spending HD and then regaining them, all in the same rest. That, and the rules say you get the benefits when you end the rest.
If you were attempting a long rest you wouldn't spend any HD because you are going get all your HP back anyway. But with your interpretation, you can actually end up with fewer HD at the end of a long rest than when you started. Because part way through you decide to spend HD in case you don't get to rest as long as you want.
I'm gonna have to go with my prior reading of the rules - you can't "end" a Short rest and still have it be part of a Long rest. Ending a rest isn't an automatic thing, the players decide when they are done and get the benefits based on how long they were resting before they ended it.
Either they ended the rest or they didn't. If they didn't end the rest hey don't recharge anything and can't spend HD to heal, but they can continue resting until they've rested enough to end it as a long rest.
If the players decide to end their rest after an hour, they get the benefits of a short rest. But once they do, they have stopped resting and will need to start again from the beginning if they want a long rest.
I've got no problem with that.
When you begin to relax/rest, you might have an idea of how long you
want to rest for, and typically you will
want to rest for either 1 hour or 8 hours, because of 5E's rest rules.
But you might not get what you want! You might be
intending to take a long rest, but get bothered by baddies after, say, 3 hours. Although you
wanted a long rest, did you
get a long rest? No.
But did you get a short rest? Absolutely you did! You need at least 1 hour of avoiding strenuous activity to qualify for a short rest, you've had 3 hours, therefore you've had a short rest.
So, when I say that after 1 hour you've had a short rest and 7 hours after that you've had a long rest, that is true. But, as you say, if you
choose to gain the
benefits of that short rest then the DM is within his rights to say that a short rest has ended (after 3 hours) and if you want a long rest you have to begin resting again. And
hope that you get 8 hours this time.
But, in the exact same situation, if you do
not choose to take the benefits of a short rest as you are bothered by baddies, then you can say that you are still pursuing a
long rest and hope that this interruption doesn't last more than an hour.
So after that first hour, that hour
might be a short rest but also
might be the first hour of a long rest. Observers cannot discern the difference by observing what you do or don't do, because any activity is either strenuous or it isn't, equally for either kind of rest.
You only need to know what kind of rest you just had at the moment you want to gain benefits from it. You don't know,
nobody knows, whether that first hour was part of a short rest or a long rest until the moment you declare that the rest has ended in order to gain rest benefits.
You rest. You get bothered by baddies. You ask the DM how much rest you just had:-
*If he says it's less than 1 hour, tough.
*If he says it's somewhere between 1 and (nearly) 8 hours, you can choose to gain the benefits of a short rest instantly because you qualify for it, but you could instead choose not to gain the short rest benefits in the hope of getting enough extra rest after this fight to get a long rest.
*If he says it's been at least 8 hours then you can gain the benefits of a long rest.
Do you have a problem with this?