This is an issue mainly on NetBSD , looks like a bug since 2009? I bet that not even it's maintainer does not use this window manager - well well no surpices if some people hate BSD's , primadonna maintainers that usually boot to windoze...
how to fix it:
- edit the /usr/pkg/bin/fluxbox-generate_menu as root
- at the line 1223 there is : USERFLUXDIR="\${HOME}.......
- remove the \ before the ${HOME}