I'm using Vim under Debian, Win Vista and WinXP (the latter two with Cygwin).

To handle tabs more easily, I mapped <C-Left> and <C-Right> to :tab(prev|next). This mapping works like a charm on the Debian machine.

On the Windows machines, however, pressing <C-Left> deletes 5 lines, as far as I can tell, and meddles with cursor position, while <C-Right> does this, too, and additionally enters Insert mode.

Question: To put it in a nutshell, how can I find out, why Vim behaves as it does? Is there a way to backtrace the active commands and keystrokes? Could there be a plugin the culprit? (I didn't install one, perhaps a default include by the Cygwin distro...) If so, how can I find it?

Additional Diagnosis:

• This behaviour occurs regardless of any existing ~/.vimrc file (is therefore not related to my above mentioned mapings) and is not inherited of some /etc/vim/vimrc, since this doesn't exist in the default Cygwin installation.

• :verbose map doesn't yield any new insights. Either nothing or my mentioned mappings appear, based on the existence of the .vimrc file

• :help <C-Left> suggests, that the default would be a simple cursor movement, which is apparently not the case.

• Vim's version under Cygwin:

  VIM - Vi IMproved 7.2 (2008 Aug 9, compiled Feb 11 2010 17:36:58)
  Included patches: 1-264
  Compiled by http://cygwin.com/
  Huge version without GUI.  Features included (+) or not (-):
  +arabic +autocmd -balloon_eval -browse ++builtin_terms +byte_offset +cindent
  -clientserver -clipboard +cmdline_compl +cmdline_hist +cmdline_info +comments
  +cryptv +cscope +cursorshape +dialog_con +diff +digraphs -dnd -ebcdic
  +emacs_tags +eval +ex_extra +extra_search +farsi +file_in_path +find_in_path
  +float +folding -footer +fork() -gettext -hangul_input +iconv +insert_expand
  +jumplist +keymap +langmap +libcall +linebreak +lispindent +listcmds +localmap
  +menu +mksession +modify_fname +mouse -mouseshape +mouse_dec -mouse_gpm
  -mouse_jsbterm +mouse_netterm -mouse_sysmouse +mouse_xterm +multi_byte
  +multi_lang -mzscheme -netbeans_intg -osfiletype +path_extra -perl +postscript
  +printer +profile -python +quickfix +reltime +rightleft -ruby +scrollbind
  +signs +smartindent -sniff +statusline -sun_workshop +syntax +tag_binary
  +tag_old_static -tag_any_white -tcl +terminfo +termresponse +textobjects +title
   -toolbar +user_commands +vertsplit +virtualedit +visual +visualextra +viminfo
  +vreplace +wildignore +wildmenu +windows +writebackup -X11 -xfontset -xim -xsmp
   -xterm_clipboard -xterm_save
     system vimrc file: "$VIM/vimrc"
       user vimrc file: "$HOME/.vimrc"
        user exrc file: "$HOME/.exrc"
    fall-back for $VIM: "/usr/share/vim"
  Compilation:
  gcc -c -I. -Iproto -DHAVE_CONFIG_H     -g -O2 -D_FORTIFY_SOURCE=1
  Linking: gcc   -L/usr/local/lib -o vim.exe       -lm -lncurses  -liconv