Chat with MSFT reveals there are many apps that keep doing that.
You are now chatting with 'Kathryn B.'.
Kathryn B.: Hello , my name is Kathryn B. with Microsoft Support. Please give me a few moments as I review the information you've submitted.
You: Hi Kathryn, I'll wait, thanks.
Kathryn B.: So if I am understanding correctly, you have an app that you purchased a while back and redownloaded today, and it charged you again?
You: Yes, that's correct. I received an email about this charge being applied to my phone bill.
Kathryn B.: I am sorry, but you will need to contact your mobile operator as I cannot view anything that is attached to that billing system.
Kathryn B.: Wait a moment.
You: I also checked other paid apps I've purchased before. Now all of them are showing up as apps that I will be paying for again! Even if it was mobile operators charging me, I am not sure why my MSFT account has forgotten all my purchased apps?
Kathryn B.: I had already started loading the billing for your account...
Kathryn B.: And I am seeing the app on here. You may want to check your next billing statement, and if it shows up on your phone bill contact your mobile operator and let them know you were already billed through Microsoft. In the meantime, I will go ahead and reverse the charges here.
Kathryn B.: Are there any other apps you wanted to download?
Kathryn B.: We have had several apps that have been charging customers again when they upgrade from Windows Phone 7, to Windows Phone 8.
You: Thanks! I was about to download Gleek, HandyScan and UKDriving license once again, but now they all show as if I never paid for them. Same applies to my games as well. I will be re-installing most apps as I had to hard reset my phone. But will I have to look out for these charges for all apps for now onwards?
Kathryn B.: Did you set the phone up on a new Live ID?
You: No, it is the same MSFT account as what I used for my Windows Phone 7 since last 2 years.