is normal,, you have install Yosemite on a Non supported MacBook, what it means, you don't have full hardware acceleration " your graphic card ",,so,, if you install Mavericks, just for info, i've installed side by side with Yosemite and Lion,,,and from all 3 OS, Mavericks was the worst,,Yosemite run's quit cool, no gliches,, only the issue with the sound control,,bisedes that he had run quit well,,never get to solve the glichs on Mavericks,,no way to solve that,,