Overview: when there are at least 2 multiselect custom fields and one of them is required, when both fields are populated and all options are removed from non-required field, the "Field is required." warning appears under the required field (when it’s actually populated)

Steps to reproduce:

1. Create 2 multiselect custom fields in “Settings” → “Users” → “Custom fields”, make only one of them required

2. Open “Users” app and open details pane for any user

3. Click “Actions” → “Edit”

4. Populate both multiselects fields (select at least 1 option in each)

5. Remove all options from non-required field

Expected result: options are removed from non-required field, no warnings appear

Actual result: options are removed from non-required field, a "Field is required." warning appears under required field

Additional info: present on snapshots and bugfests