A user noticed that this importer was not working when accessed through the Python bpy.ops API. The ImportHelper's bl_idname causes Blender to unsuccessfully attempt to place it in the bpy.ops.import namespace. This patch fixes the issue by correcting the bl_idname to place it in the bpy.ops.import_mesh namespace.
Thanks for the patch and spotting the issue.
To clarify things, it's not related to The ImportHelper's bl_idname (as ImportHelper is just a python class with bells and whistles used for inheritance) but how across Blender the operator namespace is generated (bpy.ops. + bl_idname).
It would happen with any operator having import between dots as it is a reserved word in Python.