i have never heard of this, and with all 3 pregnancies i have used a microwave, and heated plastic, glass and paper things in there, both my other children are perfectly fine, and for me i think if you worry about every little thing no-one pregnant would ever go out the house or do something in the house the whole time they are pregnant.
just think about the people who dont realise they are pregnant till later on in pregnancy, they carry on as usuall doing everything as if they are not pregnant, i didnt know i was pregnant with my son till i was almost 20weeks, and therefore carried on as usual, eating everything and drinking everything normally, i even went on fair ground rides which state do not go on if pregnant.