Strange reaction of gvim to : in a normal mode

I use gvim from xfce4 and sometimes get into a strange
situation when pressing : while being in a normal mode
leads not to the command line mode but instead highlights
the icon "Copy to clipboad".

Just now I have noted that in this situation I also cannot
see the version of my gvim via the Help menu (but saving via
the the "Save current file" icon usually works).

The output from the :version command (executed from a newly
started gvim) is as follows:

VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Sep 7 2014 11:35:08)
Included patches: 1-273
Modified by Gentoo-7.4.273
Compiled by myself.
Huge version with GTK2 GUI. Features included (+) or not (-):
+acl +cmdline_compl +diff +find_in_path +keymap +modify_fname +mouse_xterm +profile -sniff +termresponse +vreplace -xterm_save
+arabic +cmdline_hist +digraphs +float +langmap +mouse +multi_byte +python +startuptime +textobjects +wildignore +xpm
+autocmd +cmdline_info +dnd +folding +libcall +mouseshape +multi_lang -python3 +statusline +title +wildmenu
+balloon_eval +comments -ebcdic -footer +linebreak +mouse_dec -mzscheme +quickfix -sun_workshop +toolbar +windows
+browse +conceal +emacs_tags +fork() +lispindent -mouse_gpm -netbeans_intg +reltime +syntax +user_commands +writebackup
++builtin_terms +cryptv +eval +gettext +listcmds -mouse_jsbterm +path_extra +rightleft +tag_binary +vertsplit +X11
+byte_offset -cscope +ex_extra -hangul_input +localmap +mouse_netterm -perl -ruby +tag_old_static +virtualedit -xfontset
+cindent +cursorbind +extra_search +iconv -lua +mouse_sgr +persistent_undo +scrollbind -tag_any_white +visual +xim
+clientserver +cursorshape +farsi +insert_expand +menu -mouse_sysmouse +postscript +signs -tcl +visualextra +xsmp_interact
+clipboard +dialog_con_gui +file_in_path +jumplist +mksession +mouse_urxvt +printer +smartindent +terminfo +viminfo +xterm_clipboard
system vimrc file: "/etc/vim/vimrc"
user vimrc file: "$HOME/.vimrc"
2nd user vimrc file: "~/.vim/vimrc"
user exrc file: "$HOME/.exrc"
system gvimrc file: "/etc/vim/gvimrc"
user gvimrc file: "$HOME/.gvimrc"
2nd user gvimrc file: "~/.vim/gvimrc"
system menu file: "$VIMRUNTIME/menu.vim"
fall-back for $VIM: "/usr/share/vim"
Compilation: x86_64-pc-linux-gnu-gcc -c -I. -Iproto -DHAVE_CONFIG_H -DFEAT_GUI_GTK -pthread -I/usr/include/gtk-2.0 -I/usr/lib64/gtk-2.0/include -I/usr/include/pango-1.0 -I/usr/include/atk-1.0 -I/usr/include
/cairo -I/usr/include/pixman-1 -I/usr/include/libdrm -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 -I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/pango-1.0 -I/usr/include/glib-2.0 -I
/usr/lib64/glib-2.0/include -I/usr/include/freetype2 -march=native -O2 -pipe -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1
Linking: x86_64-pc-linux-gnu-gcc -Wl,-O1 -L/usr/local/lib -Wl,--as-needed -o gvim -lgtk-x11-2.0 -lgdk-x11-2.0 -lpangocairo-1.0 -latk-1.0 -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 -lpangoft2-1.0 -lpango-1.0 -lgo
bject-2.0 -lglib-2.0 -lfreetype -lfontconfig -lSM -lICE -lXpm -lXt -lX11 -lXdmcp -lSM -lICE -lm -lncurses -lelf -lacl -lattr -ldl -L/usr/lib64/python2.7/config -lpython2.7 -lpthread -ldl -lutil -lm -X
linker -export-dynamic

Any ideas how to fix it?

And whom to blame? (Except for myself, of course. :)
My first guess that something is wrong with xfce4 here.

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