CoreAdminHandler#handleCreateAction gets a SolrCore and does not close it in SolrCloud mode when a core with the same name already exists.

      if (coreContainer.getZkController() != null) {
        if (coreContainer.getCore(name) != null) {
          log.info("Re-creating a core with existing name is not allowed in cloud mode");
          throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,
              "Core with name '" + name + "' already exists.");
        }
      }