It has been officially announced on the T-Mobile U.S. support forum that the carrier is rolling out the Windows Phone 8107 update out to HTC HD7 owners. The 8107 OS update introduces numerous changes, but the highlight is the fix for the disappearing keyboard bug.
Be sure to check Zune (or the Mac Windows Phone Connector) for the notification. Unfortunately there's still no word on a 8107 rollout date for Lumia 710 owners on the T-Mobile network, though you can hack the handset to receive the update along with new firmware.
This has been confirmed by our readers who have received the update notification on their handsets. Let us know when you get yours in the comments.
Source: T-Mobile, thanks everyone who tipped us!