OK with your test account
Windows Office 2013 worked fine (Office 2010 I didn't trying since this worked)
Yosemite Office 2011+SP1 didn't work
Mountain Lion Office 2011 didn't work
With a brand new test user on my domain
Same result
So unchanged. I guess this proves only it's not something with my hosted account. So this either points at my network or both my Mac test environments.
I also tried tethering to my mobile phone rather than running through my regular router and ISP. Still the same, so apparently not them either. But of course Windows seems to have no issue running in the same environment.
Christian