Just received this in my email:
This is an update for all customers with the Tamron 17-50mm (model A16.)
Please be advised that we now have a firmware update available which will allow you to use this lens with the 70D in live view mode. If you would like to send the lens in for the update please complete the attached service form and send the lens to our address at the bottom of the form. Please include your warranty confirmation number or a copy of your receipt. If you have any questions please ask.
Customer Service Supervisor
Tamron USA, INC
10 Austin Blvd
Commack, NY 11725
The attached service form was the standard form.
I use my 17-50mm a lot, so I'm thinking of sending it in for the update.