Wow thats weird. here is some detail of the machine.
Harware
Model Name: iMac
Model Identifier: iMac13,2
Processor Name: Intel Core i7
Processor Speed: 3.4 GHz
Number of Processors: 1
Total Number of Cores: 4
L2 Cache (per Core): 256 KB
L3 Cache: 8 MB
Memory: 24 GB
Boot ROM Version: IM131.010A.B05
SMC Version (system): 2.11f14
Software
System Version: OS X 10.10 (14A283o)
Kernel Version: Darwin 14.0.0
Boot Volume: Macintosh HD
Boot Mode: Normal
Secure Virtual Memory: Enabled
Time since boot: 1 day21:45
Its using 10.10 beta3
I can’t launch 4.3 preview so this is still in UE 4.2.1
I currently don’t have my 10.9 machine handy 