Quickfix mappings sometimes leak into other buffers

[smackesey]

I've found two things with the Quickfix mappings:

• Sometimes they seem to get activated and stuck in a non-quickfix buffer. For example, the t mapping to <C-W><CR><C-W>T will be stuck, and doing a :map t to whatever seems to do nothing to fix it.
• On a related note, I've tried to override these mapping in the quickfix itself using an after/ftplugin/qf.vim and it doesn't work. Also, entering my override mappings directly as ex commands doesn't work. Greper seems to be blocking it.

Finally, it would be nice if you provided an option to disable the default quickfix mappings. Thanks!