Summary

Buffer local auto commands only seem to work when the file is passed on the command line and not when opening a file in an existing session.

Similar behaviour is exhibited with buffer local map settings as well.

Tested in both vim 8.2.2029 and neovim 6 with the same result.

It's most likely that I'm mis-understanding something but here is what I expect.

Steps to Reproduce

1. Create init.vim with only the following: au BufWritePost <buffer> echo "Hello World"
2. Run vim -u init.vim
3. :e a.txt
4. :w

Expected Result

Hello World printed in the status line

Actual Result

Nothing printed.

However if I run vim -u init.vim a.txt then it works as expected.