Arrow for sortorder not appearing on header with sortBy

[TomJannes]

What you were expecting:
To see an arrow next to the sorted column header

What happened instead:
No arrow indicating the sort direction

Steps to reproduce:

<List title={<ListTitle/>} {...props} filters={<LotenFilter/>}>
    <Datagrid>
        <ReferenceField label="Prop1" source="projectId" reference="projects" sortBy="prop1">
            <TextField source="prop1"/>
        </ReferenceField>
        <TextField label="Prop2" source="prop2"/>
    </Datagrid>
</List>

Environment

• React-admin version: 2.3.0
• Last version that did not exhibit the issue (if applicable):
• React version: 16.4.2
• Browser: chrome

[TomJannes]

If i put sortBy on the TextField instead of the ReferenceField, the arrow is visible but on sort it will use the source of the ReferenceField as sort field.

[trsteel88]

I'm having the same problem.