Steps to reproduce:

1. Enrol 4 students in a course
2. Make two users submit the assignment
3. Filter the selector by 'not submitted'
4. Press the down button on the list of users, and select each one

Expected results:

1. The student you select will be chosen

Actual results:

1. You can sometimes get another random user different to what you chose because the logic when filtering is completely screwed, see below..

This is how I found it:

I was studying this code: https://github.com/moodle/moodle/blob/master/mod/assign/amd/src/participant_selector.js#L70

And seems there is a logic bug:

1) We have an array of students and we iterate through them
2) We filter the students and only conditionally render a template for them based on certain conditions
3) But we then attach the result of a render to the original students array indexed by the promise, not taking account of the fact the index might not match the render index

For example:

[{id: 1, name: Bob, show: false},

{id: 2, name: Fred, show: true},

{id: 3, name: Ryan, show: true}]

Would result in:

[{id: 1, name: Bob, show: false, label: '<p>Fred</p>'},

{id: 2, name: Fred, show: true,  label: '<p>Ryan</p>'},

{id: 3, name: Ryan, show: true}]

I probably some work on actual steps to reproduce now..