Apparently, there are some (lots of) issues with materials applied to corona proxies.
When proxy has multiple materials, only the material on the first channel is changeable using Archicad's object properties.
texture mappings are not working correctly. Seem like some sort of 2D projection mapping was applied.
Depending on the Archicad object preview style material assignation changes on proxy geometry. When used "surface Box" or "solid box" material is green.
proxy objects material are no being updated on IR frame buffer when tweaking the materials.