You're right. Reading your posts again, i see we didn't understand well the problem. I apologize for that.
This message should appear only once time, when renderer stops, not multiple times.
This seems a specific issue with FStorm and Interactive Renderer. I just tested with V-Ray and Corona IPR and it doesn't happen (the message is not even shown).
We'll check what is happening with FStorm and will try to fix it.
-In regards to " Anyway, the dialog message is shown only when using 3DS Max on interactive mode, not in unattended render modes" !
Most professional Artists use "interactive mode" in their render engines when working on their scenes. Most 3d artists have moved on and use interactive render modes. If your plugin is not optimized for this you really need to speak to some artists to find out what features they need.
Sorry, another misunderstanding on our part. I mean 'interactive mode', as when 3DS Max is running by an human operator, not in render queues as Backburner.
I just noticed FStorm names their IPR as "interactive mode", the same term i used but for other purpose.
We'll take a look to this for our next update.