Chrome Version: 70.0.3507.0
OS: OSX 10.13.6
MR: 7018.730.0.0

Note: Mac VoiceOver only

What steps will reproduce the problem?
(1) Enable VoiceOver by pressing ‘command key+FN key+F5’
(2) Click Cast icon in toolbar
(3) Press tab to move through device list until the "Sources" button is highlighted. VoiceOver reads "Sources button. You are currently on a button. To click this button, press Control-Option-Space.
(4) Press control-option-space.
(5) Press down button to Highlight Cast desktop menu item. VoiceOver reads "Cast Desktop. You are currently on a menu item. To choose this menu item, press Control-Option-Space. To close this menu, press Escape."
(6) Press Control-Option-Space

What is the expected result? Selection is moved from Cast tab to Cast desktop.

What happens instead? Nothing changes in the UI. VoiceOver reads "Press Cast desktop".

I noticed there is a redesign of the source menu planned in bug 850570, but it doesn't look like it'll resolve this issue.