Blind transfers randomly come back to IVR

I have a system currently using Cisco 7940 phones. I am having a problem occasionally that when a blind transfer is initiated the users phone will ring but sometimes gets redirected to the IVR and other times it correctly goes to the users voicemail. All modules are up to date at this time and it is at FreeBPX version 12.0.68 running asterisk 11 which is also up to date.
Has anyone had this issue that may be able to shed some light?