RMC, yes your last post covers it perfectly.
Think about it, I give you FL180 LVL KATHY/KUMIL, then put you on a heading, and then resume you back to KATHY/KUMIL, the restriction is always in force. However I do not expect compliance at a point if I subsequently route you beyond said point without reiterating the restriction.
The greyer hairs in my head have seen all too often what happens when you give vectors after a level by restriction, my experience always works with that in mind and isn't surprised to see you sail by the point 500' high. If it is crucial, I would have already done something else to make sure we are all safe.