Urrgh...the client has decided they don't want the sub-sub-menu so it doesn't matter for this particular site but, in general, why would this have been happening?
This also plagued my older CSS MenuWriter extension on DW8.0.2 whereby we'd end up having to cheat the level with minus figures, or margins that just didn't make sense (to us anyway).
Hoping this can be ironed out. Thank you.
NJ