This discrepancy is probably due to the fact that methanol and nitromethane forms an azeotrope. First a 92%/8% MeOH/MeNO2 mixture (bp 64.5°C) distills over (close to the boiling point of pure methanol, bp 64.7°C) and when all the methanol is gone, the temp shoots up to ~100°C, where pure nitromethane is collected.
I would be led to believe that the azeotrope would distill at the same time the methanol would distill. Then, once all the methanol is gone, the temps will rise to ~100C.
So I still don't understand why the temp will slowly rise between the bp of methanol and nitro producing a distilled mixture that contains both products.
https://www.thevespiary.org/rhodium/Rhodium/chemistry (https://www.thevespiary.org/rhodium/Rhodium/chemistry)
https://www.thevespiary.org/rhodium/Rhodium/chemistry%5B/blue (https://www.thevespiary.org/rhodium/Rhodium/chemistry%5B/blue)
]https://www.thevespiary.org/rhodium/Rhodium/chemistry/alhg-meno2.html%83 (https://www.thevespiary.org/rhodium/Rhodium/chemistry/alhg-meno2.html%83)