This line is still in vimrc_example.bin, but does not seem to work anymore, at least for VIM 7.4 on Windows.
inoremap <C-U> <C-G>u<C-U>
Now in insert mode, the first time <C-U> is pressed, nothing happens. If you insert some more text, and then press <C-U> again, the newly added text is removed, and the text you originally typed is still there. If you press <ESC> and u, nothing happens -- the removed text is still lost.
Works fine, for me, in Windows gvim 7.4.629. Starting with
gvim -N -u NONE -i NONE, I set up the above mapping, and enter text:
one two three abc|
The '|' is the cursor. Staying in insert mode, I type
<C-U> to get (still in insert mode):
one two three |
Now I can type "four five six" to get:
one two three four five six|
<Esc>, then undo a change with
one two three abc
This is exactly what I expect.
If you have a different scenario that demonstrates the issue, then I suggest asking on vim_dev or vim_use mailing list about it.