Because of a minor bug in how Kael merged the 3.19 changes Firaxis made. Firaxis used a function name which Kael already was using previously, for a very similar purpose. But the purpose is just slightly different enough that it causes issues if you don't change how one or the other works, or rename one of them. It was a pretty subtle issue among a HUGE number of changes, many of which were minor and meaningless, so it was almost guaranteed to go wrong the first time through. And it isn't something which you notice right away unless specifically watching for it.