TYPO3 Core

When using the following TCA for a select field:

        'select_field' => [
            'exclude' => true,
            'label' => 'My select field,
            'config' => [
                'type' => 'select',
                'renderType' => 'selectMultipleSideBySide',
                'maxitems' => 1,
                'minitems' => 1,
                'size' => 5,
                'items' => [
                  ['Testing', 0],
                  ['Testing 1', 1],
                  ['Testing 2', 2],
                  ['Testing 3', 3],
                ],
                'autoSizeMax' => 20,
                'fieldControl' => [
                    'editPopup' => [
                        'disabled' => false,
                    ],
                    'addRecord' => [
                        'disabled' => false,
                    ],
                    'listModule' => [
                        'disabled' => false,
                    ],
                ],
            ],
        ],

Initially you should see all of the 3 items on the right side in available items. Now when you select one it disappears from the right and appears on the left (just as you would expect). When you want to change the selected one (on the left) to be another item from the right, you click an item from the right once more, the left one will not go back to the right but will disappear instead.
It only works as expected, when selecting the item from the left and using the trash icon. The items are still available in the HTML on the right side, I guess the issue is only that the elements keep the disabled="disabled" & class="hidden" in the HTML.
I recorded a short gif to showcase the behaviour (see attachment "demo") or see here: https://imgur.com/McZZUFT

I'm looking into this now and try to prepare a patch for it, but would like to have some other opinions on it as I'm not 100% sure that this is a bug or not.