There's a different bug here, where because CoreContainer loads
the cores sequentially, and MultiCoreReaderFactory looks for all
the cores, when the proxy core isn't last, not all the cores are
searchable, if the proxy is first, an exception is thrown.
The workaround is to place the proxy core last, however that's
not possible when using the core admin HTTP API. Hmm... Not sure
what the best workaround is.