Wrong source and response in form triggers - google-apps-script

Question

I set a simple workflow with a Google Apps Script. I created the script project from a form A.
Here is the workflow:
users submit a response for the form A
the script creates a new response for the form B, submit it, and sends me the edition link by email
I submit the response for the form B the script created for me
the script sends me a recap of both form by email
To do so I have programmatically set up a trigger on the form B:
function addOnNewFormBSubmitTrigger() {
ScriptApp.newTrigger('onNewFormBSubmit')
.forForm(FORM_B_ID)
.onFormSubmit()
.create();
}
The function onNewFormBSubmit looks like that:
function onNewFormBSubmit(formSubmitEvent) {
_sendAnalysisEmail(formSubmitEvent.source, formSubmitEvent.response);
}
The function is triggered but the the formSubmitEvent.source value is the form A and formSubmitEvent.response is the latest response for this form. I would expect the source to be the form B, as I attached the trigger on it.
EDIT:
Even passing a form instance instead of its ID does not work as I expect it
function addOnNewAlaysisSubmitTrigger() {
var form = FormApp.openById(FORM_B_ID);
ScriptApp.newTrigger('onNewFormBSubmit')
.forForm(form)
.onFormSubmit()
.create();
}
Am I missing something?

Answer 1

Thank you #tehhowch, the link you gave me in the comments made me think that it may work if the script is not created from the Form. Thus I made a POC creating the script from a Spreadsheet and it works.
This is the script I made: Google Apps Script
And these are the logs generated by the two functions: function call logs from Stackdriver
As you can see I get two different responses submitted from the two forms.
Now the problem is that the event is not a submit form event as defined in the documentation: https://developers.google.com/apps-script/guides/triggers/events#form-submit_4 but this is another story.
If you want to try, here are:
the spreadsheet from where I created the forms and the script (logs are pushed in the "logs" sheet): https://docs.google.com/spreadsheets/d/17pFDXlYpOjXgaN5ZsBYimrBZHl6WPcmUvMrAjAnc9ys/edit?usp=sharing
the live form A (Google sign in required): https://docs.google.com/forms/d/e/1FAIpQLSff7ISYkqLtPwtzTWw2Iwxmm4dIax7z9ye9EeLY9SxDz3vJvw/viewform?usp=sf_link
the live form B (Google sign in required too): https://docs.google.com/forms/d/e/1FAIpQLSc1HrswTr6prGxBBwy2a4Nqs1pyF7CJTjk2HafZyXsTtdnaXQ/viewform?usp=sf_link
the script : https://docs.google.com/spreadsheets/d/17pFDXlYpOjXgaN5ZsBYimrBZHl6WPcmUvMrAjAnc9ys/edit?usp=sharing

Answer 2

Have you tried to use Form as parameter instead of just his Id.
Something like that:
var form = FormApp.openById('FORM_B_ID');
ScriptApp.newTrigger('onNewFormBSubmit')
.forForm(form)
.onFormSubmit()
.create();