Because you're accessing the wrong value. Change this line:
var Ver = event.target.value;
var Ver = event.value;
That will give you the field's new value, instead of its current (ie, old) one.
Thank you Gilad. It is sadly still displaying the opposite button, and no longer switches to the other button when it should. Not sure what is going on. I'll keep plugging away at it.
If you can share the file (publicly or privately) I'll be happy to take a look at it.
I'll email it to you. Thanks so much!