I just tested Landscape material in both 4.15 and 4.16 versions.
I created Material instance and applied few textures to it, then proceeded to paint on the landscape.
In both 4.15 and 4.16, painting was fine, everything looked great. The problem happened when exiting the engine and then starting engine again and opening the level. In 4.15, landscape kept the paint and textures, but on 4.16 version painted information was kept as well on the landscape but textures inside the landscape material instance were reseted to default.
Tested this on multiple machines, with multiple landscape materials, simple and complex.