When you view a file with a space in name and press 'v' to edit it, it runs the editor with the first part of name only. (instead of 'hello world' it opens 'hello') Some more funny example is $ less "yup; rm work.c" (if you press 'v' then, it will remove your work.c) It seems that less uses system() instead of fork() & exec() ...
Setting your $LESSEDIT to "%E ?lm+%lm. '%f'" should help. I'll fix this in the Rawhide package. Thanks for the bugreport ! Karsten