lightning/datatableKeyboardMixins error

Fresh scratch org, spring 20 (also tried on summer 20 and same issue).

Seems to be a platform aura gack when copy pasting straight from the lightning-datatable docs.

Removing lines of code related to lightning/datatableKeyboardMixins allows the custom data type to be used.

For simplicity, references to custom data types passing of typeAttributes data has been omitted.

Repro steps

Clone this repo to a desired directory.

git clone https://github.com/tsalb/lightning-datatable-accessibility-issue

Create Default Scratch Org
Push
Open Default Scratch Org
App Launcher => Datatable Error (App)
- I've forced standard app visibility to hidden in the profile, there should only be one app in the app launcher

Unable to repro in Playground

Interestingly enough, this is not reproducible in the Playground:

https://developer.salesforce.com/docs/component-library/tools/playground/I93mYl8MU/19/edit

Error on load

afterRender threw an error in 'c:datatableExample' [Access denied: {"from":{"namespace":"system"},"to":{"namespace":"c"}}]

Stack Trace

le()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:29:2516
On()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:29:34982
Hn.getPrototypeOf()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:29:36342
cr()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:4:30845
ir()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:4:30907
{anonymous}()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:4:18366
Object.create()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:4:18454
sn()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:4:14668
fn()@https://static.lightning.force.com/cs68/auraFW/javascript/ozbOZt5SYUotl8he3imvcA/aura_prod.js:4:15518

datatableExtension LWC

// datatableExtension.js
import LightningDatatable from 'lightning/datatable';
import deleteRow from './deleteRow.html';

export default class datatableExtension extends LightningDatatable {
    static customTypes = {
        deleteRowButton: {
            template: deleteRow,
            standardCellLayout: true
        }
    };
}

<!-- datatableExtension/deleteRow.html -->
<template>
    <c-datatable-delete-row-btn data-navigation="enable" row-id="{value}"></c-datatable-delete-row-btn>
</template>

datatableDeleteRowBtn LWC

<!-- datatableDeleteRowBtn.html -->
<template>
    <div style="text-align: center;">
        <lightning-button-icon icon-name="utility:delete" onclick="{fireDeleteRow}"> </lightning-button-icon>
    </div>
</template>

// datatableDeleteRowBtn.js
import { LightningElement, api } from 'lwc';
import { baseNavigation } from 'lightning/datatableKeyboardMixins';
import template from './datatableDeleteRowBtn.html';

export default class DatatableDeleteRowBtn extends baseNavigation(LightningElement) {
    @api rowId;

    // Required for mixins
    render() {
        return template;
    }

    fireDeleteRow() {
        const event = CustomEvent('deleterow', {
            composed: true,
            bubbles: true,
            cancelable: true, // commented out in playground to avoid some other errors, but doesn't affect this bug
            detail: {
                rowId: this.rowId
            }
        });
        this.dispatchEvent(event);
    }
}

datatableExample LWC

<!-- datatableExample.html -->
<template>
    <c-datatable-extension
        key-field="id"
        hide-checkbox-column
        data="{data}"
        columns="{columns}"
    ></c-datatable-extension>
</template>

// datatableExample.js
import { LightningElement } from 'lwc';

const COLUMNS = [
    { label: 'Opportunity name', fieldName: 'opportunityName', type: 'text' },
    {
        label: 'Confidence',
        fieldName: 'confidence',
        type: 'percent',
        cellAttributes: { iconName: { fieldName: 'trendIcon' }, iconPosition: 'right' }
    },
    { label: 'Amount', fieldName: 'amount', type: 'currency', typeAttributes: { currencyCode: 'EUR' } },
    { label: 'Contact Email', fieldName: 'contact', type: 'email' },
    { label: 'Contact Phone', fieldName: 'phone', type: 'phone' },
    {
        label: '',
        type: 'deleteRowButton',
        fieldName: 'id',
        fixedWidth: 70
    }
];

const DATA = [
    {
        id: 'a',
        opportunityName: 'Cloudhub',
        confidence: 0.2,
        amount: 25000,
        contact: 'jrogers@cloudhub.com',
        phone: '2352235235',
        trendIcon: 'utility:down'
    },
    {
        id: 'b',
        opportunityName: 'Quip',
        confidence: 0.78,
        amount: 740000,
        contact: 'quipy@quip.com',
        phone: '2352235235',
        trendIcon: 'utility:up'
    }
];

export default class DatatableExample extends LightningElement {
    data = DATA;
    columns = COLUMNS;
}

Working example with extension commented out on datatableDeleteRowBtn

// datatableDeleteRowBtn.js WORKING
import { LightningElement, api } from 'lwc';
import { baseNavigation } from 'lightning/datatableKeyboardMixins'; // not used
import template from './datatableDeleteRowBtn.html'; // not used

export default class DatatableDeleteRowBtn extends LightningElement {
    @api rowId;

    // Required for mixins
    // render() {
    //     return template;
    // }

    fireDeleteRow() {
        const event = CustomEvent('deleterow', {
            composed: true,
            bubbles: true,
            cancelable: true, // commented out in playground to avoid some other errors, but doesn't affect this bug
            detail: {
                rowId: this.rowId
            }
        });
        this.dispatchEvent(event);
    }
}