In command line window (enter through q:), the following error occurs when trying to exiting the insert mode either through ESC or Ctrl-[
Error detected while processing function <SNR>31_CloseStackPop:
E11: Invalid in command-line window; <CR> executes, CTRL-C quits: pclose
Press ENTER or type command to continue
Well, it appears that the bug is related to autoclose.vim as reported in Stack Overflow. Not sure if we should do anything about it though.