commit https://github.com/vim/vim/commit/0ba75a9714884895b2ac09733158c47544a8dfb9 Author: Bram Moolenaar <Bram@vim.org> Date: Fri Feb 19 23:21:26 2016 +0100 patch 7.4.1360 Problem: Can't remove a callback with ch_setoptions(). Solution: When passing zero or an empty string remove the callback.

Test A:
  - file name displayed: test://bar.txt
  - quickfix claims that the file name displayed is: test://bar.txt
Test B:
  - number of window open: 2
Test C:
  - 'buftype' of the location list window: quickfix
  - buffer displayed in the 2nd window: test://quux.txt