A few days ago, I discovered that some bars of the steam-out of my electric thermo pot (which has been used for about 2 years in my house) have been melted down.

(Note: This is not the photo of my pot, it's just for the purpose of making it easier to explain what bars I mean.)
I believe some plastic dusts must have been dropped into the boiling water and of course we were not aware of it. Somebody also drank them unfortunately.
I told my father about this and tell him we should buy a new one of another brand, but he said: "All brands of electric thermo pots are like this when they have been used for some time.".
Is this true? Does the same thing happen to your electric thermo pots?