Reviewing edits this afternoon, I got this:
I'm fairly sure the "Template in use!" I have not seen before.
What does it mean?
So it works!
Ahem, it was just some test code that I forgot to remove.
That message is relatively hard to generate natively for a number of reasons. I needed to make sure I was editing the right template.
A fix will be out in the next deploy.
Fortunately I didn't use swearwords or my CC number in that occasion...