Cannot view changes to text with VoiceOver when proofreading with Writing Tools

After clicking the “Proofread” button in the Writing Tools popover using VoiceOver, only the Next, Previous, and Close buttons are visible, with no way to view the specific changes made to the text. To reproduce this issue:

1. Write some text with obvious errors and select it.
2. Select the “Show Writing Tools” action from VoiceOver’s the actions menu (accessed by pressing VO-Command-Space), and click the Proofread button in the resulting popover.