This is quirky.
For instance, if we have a 15' unconnected wall and then attach
the top of the wall to a floor at level 1, which is at 10'. The wall properties still says that the height of the wall is 15'.
Revit also shows that the "Top is Attached". Changing this height in the properties does not change anything apparently. However, selecting the wall and clicking the "detach" button in the option bar,
to detach the wall returns the wall to the actual height shown in the properties.
(even though the wall height shows incorrectly while the wall is attached, the wall area, etc schedule correctly!)