On joindiaspora, pressing cmd+left (which is usually the browser "back") leaves me in the same page. Which is more strange is that pressing the back button it works properly.
thats because they are capturing the arrow keys without checking for simultaneous modifier keys.
A more reliable way to navigate with the keyboard is ⌘+{ (back) and ⌘+} (forward). The chords ⌘+← and ⌘+→ can be captured by text input, JavaScript, or Flash.
Nice... also cmd+shift+{ and cmd+shift+} works for changing tabs.