I also see some weird behavior.
Reproduce:
1. Downloaded the latest master source code (8.2.00012 at the moment) and compile it on Ubuntu 16.04.
2. Start vim: vim -u NONE -U NONE -N -i NONE
3. Type in i to get into insert mode.
4. Type some text e.g. hello world
5. Press backspace. It works fine. It deletes the text.
6. Press <Esc> key.
7. Press A key to jump to end of line in insert mode.
8. Press backspace key and it does not work any more. Actually nothing happens.
It is interesting that everything works fine using: vim --clean
I also downloaded 8.1.2339 and compiled and the behaviour is the same.
It looks to me there is something special in:
vim -u NONE -U NONE -N -i NONE
compared to:
vim --clean
But it looks like setting (I have this in my .vimrc):
:set backspace=indent,eol,start
fixes all of this problems.