HTTP Response Splitting Exchange 2013 iOS Calendar emails being blocked

Hello All!

Was wondering if I could get some help. I'm currently running FortiWeb-VM 5.35,build0463,150407 i'm currently experiencing an issue with Exchange 2013 and iOS devices 8.0+.

When we send a calendar invite or a response to a calendar/meeting invite a Alert_Deny for signature Generic Attacks-HTTP Response Splitting: Signature ID 050130001 gets triggered.

Now I don't want to just disable the signature if possible, but was wondering if anyone has faced this and has found a way around this without compromising the security of the device.

Thanks!