I am trying to map <C-N> and <C-P> to behave differently when pumvisible() returns true, but Vim seems to completely ignore this. E.g., if I create this unconditional map (a much simpler one than what I wanted):

inoremap <C-N> <C-C>

pressing ^N normally stops insertmode, but when popup is visible, Vim never executes the map. This may be true for <C-P> also, but the same is not true for, say <Up>.

inoremap <Up> <C-C>

Using the above map, pressing <Up> arrow always stops insert mode, whether popup is visible or not. Is this a bug? I tested by starting with -u NONE option to avoid any other interferences.