Giving any operator three or more levels results in it being treated twice. For example, changing "mesh.primitive_gem_add" to "mesh.primitive_gem.add" results in
MESH_OT_PRIMITIVE_GEM_OT_add. This crashes Blender whenever the operator appears in the UI and prevents it from being accessed directly.

The problem is WM_operator_bl_idname(), which searches for '.' characters and formats the string regardless of whether it's been processed once already. (Or, arguably, that idnames with multiple dots make it that far at all...)