In-App Purchases don't persist between app installations

I have a question for developpers which uses Windows store in-app purchases.

I create some in-app purchase in my Win8.1 universal app to unlock(make disapear) ads in my application. I am currently testing IAP with a beta version (hidden app).

I do the following to reproduce my problem :

install beta version of my app : I see ads
buy license "no ads"
confirmation that everything works as intended : no ads are displayed
uninstall the app
install the app again : I see ads , but I should not !

So, the app uninstallation loses all the IAP licenses bought, but for my app, they must persist between installations.

I searched a lot concerning this but to with no clear answer :

I've read about receipts (here and here) but it seems it's for Consumable IAP and not necessary for Durable IAP.
this might be because it's a hidden (beta) app ?

Can someone confirm or refute these guesses? Must I use receipt for durable IAP, too?

Solution

To answer to my question, I have contacted MS dev support, this is the answer :

"To answer your question because it is a beta the IAP is one time only so every time you uninstall and install you will be promoted to buy the IAP again. In a beta each time you reinstall the app the license data is cleared and it has to be purchases again. But once the app goes live you will not have that problem."