If I use "newpage" to split the diagram, unused participant are included in other splitted diagram

Question

Hi

I used the "newpage" keyword to split the diagram into several parts.

If we have, let say 3 participants Bob, Alice and Frank.

In the first part, Bob and Alice are part of the process, but in the second part, the process just involved Alice and Frank.  In the generated diagrams, I see the three participants in every part.  

How to prevent that ?

Thx

Francis