I do not have information on the bottles--plastic or glass. However, I nursed my little girl for 13 months, and my lactation coach encouraged me to never heat milk/formula in the microwave either way.
I pumped quite a bit b/c I had a lot of milk, and after freezing the bags, when I was ready to use them, I would place them in a cup of hot water, and let it naturally thaw and warm. She said that milk does not necessarily need to be very warm for your baby to enjoy it, and that heating in the microwave takes out the natural components as it heats. When nursing, she said the milk is just barely luke warm, so when not nursing, it should be the same.
When I stopped nursing her, I finished using the pumped milk I had, and by the time she was 16 or so months old, I warmed regular milk in a glass of hot water too, as directed.
I hope this helps, as everyone is different. The point my lactation coach made was to do the same with the milk whether nursing or not. And my daughter never had any difficulty with the transition, partly b/c the temp was always the same!
Good Luck!