HTC rolled out an update to the HTC One recently which fixed a number of issues, although the update also created an issue with the HDR camera feature.
T-Mobile has now released another software update for the HTC One, the latest update is designed to fix the issue with the HDR Camera feature.
The latest HTC One software update for T-Mobile is available as an OTA update, you can check to see if it is available for your handset from the setting menu on your device.
Source Android Community