I have to agree, if this is how it works and they label a deposit the same as purchase then this is not a very nice thing to do.
As you have described to deposit usually means that you will also withdraw it after a set amount of time, however in this case as soon as you have "deposited" the ingots they pop up in the ingots event as spent.
I would like to get a legit response from oasis explaining how on earth this deposit turned out to be a purchase in their mind, if that is truly the case.