Mentions prefix does not work in the new issue view

Summary

In the new issue view, the "[~" prefix for prompting the Mentions feature no longer works. This means that the only way to bring up the Mentions window is with the "@" prefix or with the editor.

Steps to Reproduce

1. On any mentionable field (ie: comments) type [~

Expected Results

In the old view, the Mentions window would pop up with a list of users to tag which would be expected in the new view as well

Actual Results

Nothing happens.

Notes

This is strictly in the new issue view. Using the "@" prefix instead works as expected in both new and old view. Manually inputting the proper markup for the Mention function will simply be added as plain text.

Workaround

No actual workaround, use "@" instead.