Some do have a problem with this one but Thermomixer did some testing. I know there is a lot to read in this thread but if you have the time Generali, have a read to see if you can pick up any hints. This is Thermomixer's deduction
Ok - THE ANSWER - it is the SPEED !!!!!!
I started making as per the instructions and after 20 minutes it is all going brilliantly.
Then I decided to experiment. If I turn the speed down to 3 then foam started swelling up inside like a volcano and if you turn the speed back up to 5 then it won't overflow !!
So, tried again few times and I AM CONVINCED - if it goes at greater then 4.5 it is OK - but slower and you are likely to have a mess.
It is fun turning it down and then stopping the overflow by speeding it up.
Hope you give it a go Bel - even try just with a small amount of milk without the rest to begin - set it to Varoma and speed 3 and watch - as it starts to foam turn it up to 5.