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-10.9x...../C5.5/6.5/7.5/C8P
On the side of a volcano in the middle of the Pacific Ocean.