Wow! That's strange to say the least.
Sounds to me like some corruption (either download or install) goin' on.
I would say try re-downloading and re-installing.
If yer gear ain't breakin down, you aint workin' much.
iMac i7 2.8Gz 16GB 10.9...../C5.5/6.5/7.5
Mbook 2.4Gz 4GB 10.7.5.../C5.5/6.5/7.5
On the side of a volcano in the middle of the Pacific Ocean.