Yes.
I had a conversation with a Siemens engineer either last year or the year before.
About the exact same problem with early Sabroe screws with variable speed drives.
I can't remember exactly what they did to cure the problem.
But I know a man that will likely remember, so i will speak to him next week and see if i can come back to you on this one.
I think it is down to the style of the bearing and there being no route to earth for the induced voltages.
As you rightly suggest Gerben.
Grizzly