I think this is a bug, but I took a rest with my party. I said I would use the rations and boom, 5 rations are used after rest.

But guess what, my characters did not get healed, at all. Is this a bug, or have I misunderstood something? The camping supplies' description clearly states that I will get healed by using them

There are certain places where the party cant rest for some reason.
The rest button will be changed to a "pass time" button instead and you still consume rations, but get nothing for it.
No idea why that is a feature, but it is.

I noticed you cannot "rest" without "guards".
At least one character needs to guard or you can only pass time?

Rest will be changed into Pass Time, when you are in a dungeon and you do not select "Use rations" because you can not hunt in dungeons. If You can't rest, you won't be able to pass time neither because no rest means no possibility to set up a camp.

That was not the case. This was out on the map, not in some dungeon

When you resting out on them map sometimes you have to select 'use rations' to. I had problem becouse game isn't clear about it, and about how to do it.

And if you don't select it you just skiping time instead of resting.