I may be having the wrong idea about AppCompat, so please enlighten me

I've given it a shot, actually uninstalled and reinstalled JDK and the Android SDK including all the bits that
@corwin42 mentions in
the AppCompat post. I added the latest AppCompat library to
the CompactActionBar demo project as well as, in the Main (and only) Activity:
Code:
#Extends: android.support.v7.app.AppCompatActivity
and in the Manifest Editor:
Code:
SetApplicationAttribute(android:theme, "@style/Theme.AppCompat")
But the result is the same. I had the (possibly completely wrong) idea that AppCompat would sort of provide stubs that would cater for changed signatures to provide backward compatibility. Am I missing something, or did you perhaps mean 'use the AppCompat ActionBar object instead of Compact ActionBar'?
I'm attaching the exported project; any pointers would be greatly appreciated!
On a sidenote, I can't help wondering (feel free to refer me to a document or to tell me the explanation would be too long) why this didn't happen with any B4A version up to and including 6.50 but does now with 6.80 - it could be useful to know, e.g. to potentially avoid future pitfalls.
Thanks!
(Some version numbers: JDK=jdk1.8.0_121; SDK=android-25; B4A=6.80; Android on phone=6.0)