Gnumeric is calling:

 gnome_preferences_get_menubar_detachable ()

When it wants to check whether its toolbars should be
detachable. But there is a separate preference for
this: 
 gnome_preference_get_toolbar_detachable ()

So, if in the Look and Feel/Applications capplet you turn
off "Can detach and move menus", you make it impossible
to move toolbars in gnumeric, even if "Can detach and
move toolbars" is on.

The fix is simple - just change all instances of 
get_menubar_detachable() in gnumeric to get_toolbar_detachable.