There's some recovery partition issue with 167X. If i install a fresh copy of OSX i get the recovery partition, but if i clone it with CCC to another drive - i can't see the recovery anymore (not with F12 and not with alt). The partition is there and i can see it when booting this hard drive in macbook pro. Didn't have this issue with previous releases.
There's an interesting Time Machine issue in 1669: I have a 256GB SSD with 10.10.5 and a pair of new 3TB Seagates (all internal SATA) and if i backup the SSD to one of the 3TB drives - after reboot the computer freezes on American Megatrends logo, i can't even enter the BIOS. Nothing helps until i physically disconnect and format the backup drive. Did anyone else experienced anything like this?