Operating system: MacOS X 10.14
Graphics card: intel HD Graphics 4000
Worked: 2.80 Beta, 46ac288a9306, 2019-02-08 4:22, Branch: blender2.7
Short description of error
Material preview in Shading view shows distorted image if Principled BSDF node has Clearcoat parameter set greater than zero.
Exact steps for others to reproduce the error
. Create new generic scene with cube.
. Go to Shading view
. Select 'Principled BSDF' as Surface as material
. Open the Preview field if not already open
. Adjust Clearcoat param of PBSDF node in nodes pane.
. Set back Clearcoat param to zero (0)