So I was purchasing a group the other day, and it wouldn't let me buy the group because I was using a group name that was already taken. I finally managed to buy a group but I found out that in the 'Purchases' tab it showed that it had charged me for each group I tried to buy but couldn't because the name was taken. It hadn't actually taken my ROBUX but it said it had.
This bug happens every time I've tried. It's simple to reproduce. Just create a group with a taken name and when it says you can't purchase it because the name is taken go to Trade>My Transactions>Purchases and it should say you've purchased the group.
The bug happens on the main site. Creating the group on https://www.roblox.com/groups/create and checking purchases on https://www.roblox.com/my/money.aspx#/#MyTransactions_tab
I experienced this issue using Google Chrome.
Screenshots of the bug:
I first noticed it on the 4th of June 2017. I don't know how long it's actually been happening though.
Hope this issue gets resolved.