Update:
I have checked to see if this behavior is also in the preceding version (4.2, build 1944) and it would seem that both jw-player and the adding of users are each working ok.
Hopefully I have found something constructive and am not just wasting everyone's time.
Edit:
It would seem that there is some problems in my case migrating from 4.2 to 4.3 using tomcat6.
By manually deleting all tomcat6 cache items relating to subsonic I have the correct jw-player displayed and users can be added and removed without any problems. Interestingly I have only just found the email field in the user management page.
I have been musing that tomcat6 may have been holding some data in a cache and in the absence of a change of container name (between subsonic version upgrades) it just kept using the same data????
Please ignore my ramblings, It would seem that subsonic has not failed me yet! Great project!