Sorry - I think I forgot to include documentation for that change in the iOS 7 update change list.
Actually, it was by design. I had a number of users say the old way was counter-intuitive to them. They wanted the timestamp to occur when they invoked the entry window. They cited some pretty good examples, I did a little testing, and gave in - swapping the behavior in the iOS 7 update. The thinking is that when you invoke the window, you’re reading a temperature that is likely to change a number of degrees by the time you get it typed in, so I saw the advantage. Since then, I’ve had some feedback that my original method fit some people’s workflows better.
I think what I may do today is pop a preference setting in to choose which mode you use. Programmatically, it’s a very easy thing to do and won’t take long to do on my end. I'm uploading a maintenance release either today or tomorrow to fix a Bluetherm Duo data logging issue. I plan to include this fix on that update, so it should be live soon.
Thanks for posting