WindowMaker launching another instance from dockbar

For launching another instance of an application by clicking on the icon in the dock, hold down Ctrl.

I have two xterm apps in the dockbar, one for a todo-list and one for "done" (aka knowledge base):

xterm -class UXTerm -title done -u8 -g 50x40 -e vim /z/txt/txtcvs/done -c $

xterm -class UXTerm -title todo -u8 -g 50x40 -e vim -O /z/txt/txtcvs/todo -S /z/.vim/todo-macros.vim

If xterm is running, it is impossible to launch "todo" without Ctrl. Or you can run more instances of e.g. Firefox by this...