I've mapped control-m to start the Syntastic check mode (Active/Passive)
nnoremap <c-m> :SyntasticToggleMode<Cr>
But in normal mode, when I tap the return key, it also toggles the mode. When removing the mapping line above, the problem is off. Any clue of that?
Remember that some key combinations are equivalentin the duplicate question.
Returnequivalent, see Terminals are Weird, and if you're wondering why CTRL-M and
Returnare still equivalent, see this discussion on the vim_dev list.