If is not theme dependent, then must be a glitch in the exif module because this information is not listed no matter the camera(Nikon model) or the lenses I've used. I have pictures on my website taken by Nikon D40, D80, D90 or D7000 and with lenses as Tamron 28-70, Nikon 10-24, 70-300, 18-55... etc. I've readed that the Nikon exif model is supported. It is possible this error to be generated by Lightroom ? No matter the camera or lenses, all images are exportd from Lightroom.
I will try and use a Nikon dedicated software to verify and I'll be back with an answer.