This is Archicad's new aesthetic clash detection system. The furniture does not go well with your design.
Just kidding.
Does the same happen when you put furniture on top of the tiled area?
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"