Load JAXBContext with the Klass-Classloader - avoid using the ThreadContext classloader, which is used when no classloader is specified
Guard query refresh by adding one more pair of setBusy(true)/setBusy(false) pairs around the real query invocation

setBusy reacts like an semaphore - only if equal many setBusy(false) are recorded as setBusy(true) were invoked, busy is released.
Adjust to bugtracking module convention: An unset query name is not the empty string, but needs to be null
Better integrate issuetable