Timewalk : Cast Twice property doesn't work

The Timewalk spell gem is capable of appearing with the “Casts Twice” property.

However, when I use this Timewalk gem on a target creature, I get the following result:
(Here Creature A is the currently active creature, and Creature B is the next creature in the queue)

Creature A : Casts Timewalk (with “Cast Twice Modifier”)
Target Creature : Moves to the top of the Action Queue
Target Creature : Does nothing (as expected, Tmewalking creatures do not act)
Target Creature : Returns to original position in Action Queue
Creature B : Starts its turn

That is, I would expect the target creature to take two extra turns (with no actions) but it seems to only be doing one.