This was probably the mistake. The other handlers are named RenderMaterials as well but this actully has no affect apart from on stats, due to a (counterintuitive) disconnect between the registration name and the name of the request handler. Will be tested very soon and reverted if this still does not work.
= OpenSim.Region.OptionalModules =
The modules in this part of the OpenSim source tree are candidates for
forge. For the time being, until we have reached consensus on
(a) what should be core or optional
(b) that we have reached a stable API
(c) how to maintain optional modules
we will keep these modules in-tree.