I think you get hung up about the "functionality" of a tag. The CSS "display:table" does not change the semantics, only the visual layout of an element. The "functionality" effects you describe are just visual layout effects on the elements, there are no semantic changes.
You are correct that element sizes outside of the parent-child relationships can effect each other when using table-layout. This is the whole point of table layouts in a nutshell. This is not special for tables. Other layout properties like float also affect the placement and sizing of other elements outside of parents/children. The effect is purely visual layout - its not like declaring an element as a table suddenly turns another element from a form into in image. There are no semantic effects on other elements.
Vertical alignment and border collapse are also purely visual effects, and again there are many other examples where the css display model will affect the interpretation of other css properties. I.e. changing the display from 'inline' to 'block' or to 'inline-block' will change how border, padding and margins are interpreted. All of the available values of the display-property can be said to switch the layout into a different mode.