In Evil, Ctrl-o is not working like in Vim

When I press Ctrl-o in insert state, then press :w, Evil remains in normal state after executing the colon command. When I press Ctrl-o in Vim, then the :w command, the command is executed and Vim returns to the insert state. In other words, in Vim, Ctrl-o executes one command and remains in insert state. In Evil, it remains in Normal state after executing the command. It would be fine if Ctrl-o had exactly the same behaviour in Evil and in Vim. Is there any reason for this not being so?