Siege engines can't cancel unpacking

[elexis]

See ​https://wildfiregames.com/forum/index.php?/topic/24979-catapults-cant-move-in-standground-mode/ for a GIF and the original report.

Reproduce:

1. Start a singleplayer match with 2 players with siege engine civs (athen, ptol, seleucid, mace...) on a tiny map 
2. Type "gift from the gods" cheat
3. Build the building to train the siege engine and train a siege engine
4. Move the siege engine to neutral territory. The siege engine is still unpacked and still in the default standground stance.
5. Type "gift from the gods" cheat (so that packing isn't instant anymore)
6. Press Alt+D and switch perspective to player 2
7. Type "gift from the gods" cheat
8. Train some attackers, and let them attack the siege engine
9. Switch perspective back to player 1 
10. Observe that the packed siege engine starts unpacking on it's own as it was attacked by an enemy.
11. You want the siege engine to retreat intead of continue to unpack and attack. Therefore you click on "cancel unpacking".

Expected behavior: Clicking on "Cancel unpack" stops the unpack process and allows the still packed siege engine to process move orders. 

Current behavior: Clicking on "Cancel unpack" resets the the unpacking progress bar to zero, but the siege engine starts the unpack progress again on its own.

The user has to wait to wait one full unpack cycle and then one full pack cycle to move the siege engine that was packed already. 

It's new in Alpha 23, is it related to ​Phab:rP21630, ​Phab:rP21784 or ​Phab:rP21786?

It is said that setting the Passive stance avoids the problem.