Tamy, there’s no way to go back without simply using b15. That being said, the polyline issue looks like it’s a mac-specific bug and we hope to have it fixed soon. Keep your eye #945:https://github.com/AnalyticalGraphicsInc/cesium/issues/945
Tamy, I’m sorry to hear you are still having problems. Can you provide us the OS, video-card, and browser version for the machine you are still seeing the problem on. Also, be sure you have the latest video card driver.
Also, as a shot in the dark, try clearing your cache or if you are in Chrome, running in Incognito mode to see if that has any effect.