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
