Spawn Champions are unable to undo actions at Shop after spawn dies. (Shaco, Zyra, Heim, Etc.)
Hello, hello; I've been meaning to report this bug for quite awhile now to be honest but hadn't gotten around to it, but for any type of spawn based champion, such as Zyra, Shaco, Heim, Malz, and other champs of the same form, all lose the ability to undo actions in the Shop Menu after one of the champion's spawned creature dies or disappears.
If any turrets Heim has out dies he can no longer undo, if Zyra spawns plants that die she can no longer undo, or if Shaco (or any other champ similar) has a box down that gets triggered he can no longer undo; etc, etc. The interaction is exactly the same regardless of the champion; once a spawn dies, you've lost the ability to undo any previous action in Shop.