Pass multiple ids through rule action "Save PDF as file on server"

I'm trying to save a single pdf of a list of nodes passed through VBO view to a rule component.
My view and PDF display with contextual filter works as intended as I test it by setting the VBO option "Pass ids as arguments to a page" or by opening it directly by URL with some dummy id values as parameters.
But I wasn't able to do the same creating a rule component that opens the same view saving the resulting PDF .
I correctly created a rule component (fired by VBO button in a view) that accepts a list of nodes as input, loops through it concatenating every nid to a single string and then passes it to the final action "Save PDF as file on server".
But after many attempts I discovered that if I pass (or even write manually, just for test purpose) node ids one per line, as the action configuration GUI suggests, the pdf shows only the first node. If I write node ids separated by a + sign, it works.
I checked the code in views_pdf.rules.inc and set_arguments() needs an array. The fact is in my case that the parameter is one with multi values, but probably the configuration GUI is tricky and causes misunderstandings.
Hope it helps.
Thanx for attention