JBoss Developer provider (see https://github.com/jboss-developer/www.jboss.org/blob/master/_dcp/data/provider/jboss-developer.json) uses data_jbossdeveloper_demo however name of index resp. file in https://github.com/jboss-developer/www.jboss.org/tree/master/_dcp/indexes is data_jbossdeveloper_demos.json.

It's typo. It should be data_jbossdeveloper_demo.json

This breaks clean installation because proper index is not created during init_indexes script. Then mapping is not created (because of missing index) and general DCP search doesn't work as well (because of missing index).