I used an oil flask on brazier at watch barracks, and it disappeared. It might have something to do with me using it on those, but it has 'unlimited use/day' on it. So I assume that this might be a bug.

The item is unlimited uses but I think the script destroys it.

Clickable braziers light when you click them...

yeah I know that now, just thought I would give it a try.

Oil flasks should function as single-use items to create campfires.

They now do so properly.

Fixed.