Make sure to thank him a few posts down.
Nice find - a lot of people have been complaining about this problem recently.
For anyone who doesn't want to do the above, simply copy and paste this code into the address bar when you're on the relevant Google Play page...
Prerequisites : Desktop/Laptop computer Browser with ability to "inspect element"
Must have a valid credit card and a registered wallet account for this to work
And must be able to follow directions
Thank - jollyb for Finding/Translating THIS fix he found on a croatian forum.
1. Open Google play (Market) in Chrome browser (on your desktop/laptop) and find the wanted app (best would be that you backup the app via Ttitanium backup if you can, and uninstall it)
2. 'Right-Click' on "PURCHASED and select Inspect element
3. Above the selected row you'll see [data-ispurchased="true"]
4. Change "true" to "false" and press ENTER
(Having problems with downloading another app? Change the inspect element back to "true", app should start downloading now)
5. Click PURCHASED that will open the popup to buy via Google Wallet so you can purchase the app.
Tested on Google Chrome browser, please post if you've had success with/on different browsers.