Hi, the same username is in 3 different realms though there are 7 realms in all. I have actually received a response from Cisco TAC, it's just take several weeks to get this far and thought I'd put the query into this forum to see if any other's had similar issues.
The answer from Cisco is that the FMC v6.1 does not support more than two realms, in a single context, and even support of two realms is a workaround, with the first realm having the source subnet referenced as "0.0.0.0/0" equivalent to "any" and the second realm having the default "any" source subnet
A feature request has been submitted to Cisco to allow more than two realms with no workarounds but it's new so will be some time, if at all, before this feature is provided.
Hope this helps any one else reviewing this product.
Regards