This is a left-over from JDK-8274061 (skin cleanup to allow replacing the skin without memory leaks/bad side-effects): Tree-/TableRowSkin register listeners to fixedCellSize that are not really needed - they do nothing but cache the fixedCellSize. This should be replaced by a live lookup of the value when needed, similar to the fix of JDK-8246745 for ListCellSkin.

Doing so led to visually incorrect initial state of the horizontal scrollbar (thumb covering nearly all of sb's width) for many columns and fixedCellSize enabled. The underlying reason is that the initial sizing depends on fixedCellSizeEnabled being false (which is a misbehavior related to broken horizontal virtualization, JDK-8185887)