Issue #1

I built a number of houses in my level 1 city, 4 to be exact. Before I reached city level 2, I researched housing. Upon my city entering Level 2, none of my houses were upgraded. 

Issue #2

While using the same city from Issue #1, I researched Estates before hitting City Level 3. When my city finally upgraded, instead of upgrading the buildings, all of my huts were removed and my cities population was set to 20. 

Issue #3

While using the same city from Issue #1 and #2, I attempted to replace my recently destroyed huts with the estates that I had researched earlier. But estates were not available in my build list (they weren't visible at all). Only houses and slums were in my build list.