Umask doesn't change after reboot
I can only guess but I think it's an error in 10.10.3 which is solved in 10.10.5 (or maybe 10.10.4) because none of my 10.10.5 hosts show your 10.10.3 behavior.

So I recommend to update to 10.10.5/4.1.5.

BTW the integer in /var/db/com.apple.xpc.launchd/config/user.plist is calculated by converting the three binary "triplets" to a decimal number:

002 = 000 000 010 =   2
022 = 000 010 010 =  18
666 = 110 110 110 = 438