Syncing external device with Cubase Midi Clock. HELP!

Hey all, new to the forums, but the wealth of knowledge is amazing.

Here’s my problem:

I’m trying to sync the tempo of my AXE FX II with the Midi clock (i.e. tempo in Cubase 7). The tempo syncs at first (I can change the tempo track and visually see and hear the tempo reflected on the AXE), but after about a minute or so, it stops responding to any tempo changes and drifts out of sync. If I restart Cubase it syncs again and then eventually doesn’t.

My AXE (via USB) is setup with a Fireface 800 as an aggregate device in Mac OSX 10.9.1. I’ve set the AXE to use global tempo. Set the patches to use a subdivision of the global tempo. USB adapter mode is ON, Midi Channel is OMNI. In Cubase I’ve set my Synchronization Setup to Internal Timecode (so Cubase is the Master Clock) and the MIDI Clock Out is set to go to the AXE MIDI In.

What am I doing wrong? Is this a bug? This is driving me mad. Just want my AXE FX to sync with my Cubase BPM. I’ve tinkered and researched for a while and can’t seem to fix it. If anybody has any tips, they would be much appreciated.

Think I may have solved the problem, through a work around. It appears that the AXE FX USB driver is the culprit. When I routed the midi clock from the midi out of the fireface into the midi in on the AXE FX it seems to be stable.