[from a beta tester]
“Under 4.0.0.283, OS X with full keyboard navigation enabled, some of the controls can’t be tabbed into, and the tab order is kinda screwy.”
Thank you, we are aware of this issue and have some improvements planned for the next build
This has been improved greatly in 4.0.0.284. Under OS X, with Full Keyboard Navigation enabled and set to "press Tab to move keyboard focus between: [All Controls] " you can now use the tab, arrows, and space bar to select most UI widgets in the main editor window.