I've seen something similarly wacky with city defenders being able to wander outside of a city.  I was attacked and somehow after the battle there seemed to be duplicate defenders on top of each other such that I could take my City Militia and walk around with them as a stack outside the city walls.   Not sure how this happened but I've seen it happen two separate occasions.

Both happened to me several times.

And I can 'duplicate' my army right after a defensive city siege (Game version, 1.3 legendary hero):

As you can see from the following figure, I moved out my army after a siege, instead of getting one army, I got six.

If I click the 'ARMY' panel. You can see that they are all duplicates.

Thankfully, it only take a reload to fix this glitch.

I've also noticed that if I take an AI city and then don't garrison it, relying on the inbuilt garrison troops, then if anything attacks the city, the city will fall without a fight. In other words, it's as if the city has no defenders at all. Is this as designed? Is this the same thing that the rest of you are seeing, i.e. city defenders disappear after one battle, and that even applies city defenders after the city is conquered? In my last game this happened to me even though there were maybe two or three turns between capturing the city and the cities being taken by single attacking units, with no combat at all.

Clearly the garrison units re-appear at some point, I have wondered if this is because I play quite long sessions without reloading, and whether the garrisons would reappear if I reloaded.

So this is another example of the AI having an unfair advantage over the player instead of better Artificial Intelligence?

Cool.

Did they fix that in the 1.4 beta patch?

Can this seriously get looked at balanced out? The fact that city militia defend only one city assault, and then disappear even if they don't die, is pretty ridiculous. Whats the point of even having them if they only fight one army and the AI brings 6 or 7 to siege in one turn. 

Just to play devil's advocate - what should happen to any milita defenders that are wounded and/or killed in early "rounds" in later "rounds"?  Should they enter the next fight at full health, or should they start off injured (or dead, as the case may be?)

From the perspective of maintaining verisimilitude, they should retain injuries (or stay dead), but probably from a mechanics perspective (this is a handwavy design thing to prevent the old-school option of actually building and stationing lots of low-level units in cities to prevent otherwise non-threatening random wandering mobs from destroying the city)