Rapid casting does not work on "Cast on ***" skills

Despite the fact that game reccomend to use this support gem - it does not work

My currect cast on crit have 110 max energy for my Arc spell with 1.18 cast time. If i put rapid casting in it? tooltip for arc changes to 1 second cast time while cast on crit tooltip for max energy stays at 110.

Same goes for supports lowering cast or skill speed.