Last night, Microsoft released a new Xbox One build to its preview users. This preview build includes a bug fix that resolves an issue issue which sometimes prevented users from purchasing the full game after participating in a free trial weekend. It also includes fix for an an issue which could cause managing DLC for certain titles to crash your game collection.
UPDATE DETAILS:OS version released: rs1_xbox_rel_1608.160826-1142
Available: 6:00PM PDT 8/27 (1:00 AM GMT 29/8)
Once the update is available, you can update by launching the Guide and navigating to All Settings > System > Console info & updates.