OK, it appears that you are correct.
I logged into Sample Company as 5/31/2015, 8/31/2015, 9/30/2015 and the behaviour is as you documented here.
In each case, if I create a new GL batch, the period defaults to 12 (as expected).
it is just the various reports that follow the month that I signed in as.

This being the case, I would not bother to make any suggestions to R&D.