Patch Question: "The cost to double produce a number of Mongol units has been fixed"

In the Winter Update, the devs put “The cost to double produce a number of Mongol units has been fixed” under Mongolian bug fixes. The wording here is rather vague, so I’m not sure if I’m alone in my curiosity; what was the original bug and what, exactly, has been fixed? Are the prices different than before? Production times? Was this only affecting some units or all units?

Thanks in advance for any answers you might be able to provide.

The cost for double unit vs single unit was inconsistent previously.