Duplicate emails

Hello list,

Some of the emails I receive are duplicated in Kmail. See screenshot attached 
for some example.

Not all the emails received are duplicated; it happens frequently, but not 
always. I could not find any pattern for the duplicated emails; However, I am 
the impression that it is related with emails coming from mailing-lists.

If I use the "Delete duplicated emails", one of the duplicated email is 
deleted.

I am using Kmail 5.2.3 from debian testing.

Does anybody have an idea of what is going wrong? How can I fix it?

Thank you.

Best regards,
Gurvan