The Spacebar keyboard shortcut only works if you're still focused inside of the session list. If you've clicked anywhere outside of the session list pane, pressing spacebar won't get passed to the session list.

For example, if you've clicked into the inspectors pane, spacebar will get sent to that pane, not the session list. To get back into the session pane (where spacebar would work), you have to either click back inside the session pane, which would change the session selection you were on, or employ some roundabout shift-tab trickery, like clicking the furthest left tab closest to the session list, then shift-tabbing a handful of times to get back into the session list. But this is pretty kludgy.

It'd be great if there was either a keyboard shortcut to switch focus back into the session list, or at least a tabbing shortcut multiplier which switches between panes, e.g., if Ctrl-Tab switches tabs, Ctrl-Alt-Tab switches between panes -- though this particular combo wouldn't work, as it's already claimed by Windows OS.