Seems you missed the comment on the AS7 issue you reported..
Have you tried using:
@Resource(mappedName = "java:/module/UserTransaction")
That seems to work fine with AS7 on my end.
No wait, sorry, i missed the CDI part of this.
Weld is overriding the mappedName in it's ResourceInjectionService, basically saying
if(injection point type == UserTransaction) lookup java:/comp/UserTransaction
The Arquillian testcase is not a EE component and has no comp namespace associated with it so it fails.. Not sure if this is by spec or not, but checking with the Weld guys.
It is fixed in Jenkins build 1485
I've the same problem with the Resource-Injection of SessionContext in a pojo.