Unexpected behavior for non-prefix key

[yangchenyun]

Define a key with one char in another prefix key is not allowed. But the expected behavior will be p binds to one and ps binds to another cmd.
"p" 'projectile-switch-project "ps" 'smex

This situation could get worse if evil-leader/set-key-for-mode is used.
(evil-leader/set-key
"p" )
(evil-leader/set-key 'minor-mode
"ps" <another_cmd>)

Then the original "p" bindings will be overwritten without warning.