Unexplainable Depth increase

I am putting together a rather complex movie and wan’t to be able to control the depth of the various parts in it. However the highest depth of it suddenly rises by 20000 and i dont understand why - Around the point where it happens i include a combobox component - Now my question is - could that be what is causing the sudden leap in maximum depth - and if so what can i do about it?

Any other ideas as to why this happens?