If active buffer is modified, `:AirlineRefresh` apply `normal` highlight
instead of `normal_modified` highlight.
No particular config is requiered to reproduce this bug.
I see this bug with option `g:airline_skip_empty_sections` set.
Add any modification at the active buffer return to normal mode,
**do not save** and wait a few seconds, you can see highlight change to
normal but file is modified.
Without option `g:airline_skip_empty_sections`, add any modification at
the active buffer return to normal mode and type `:AirlineRefresh` you
can see change to bad highlight .
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