Vlad To clarify, this behavior was recorded in the newest beta. Basically, the way that safari works is that the sidebar is shown for the start page, but not shown for other tabs (that are on other websites) UNLESS specifically toggled in one of those tabs. So whether the sidebar is shown or hidden cannot be a global property (as in, applying to every tab), it must distinguish between whether that tab is on the start page or not.
Additionally, the Orion start page is not remembering the sidebar show/hide preference, it always reappears. In Safari, if I toggle the sidebar to hidden on the start page, that preference is remembered for all new tabs and every time I navigate back to the start page. That is not the case currently in orion. Every time I switch back to a tab with a start page, regardless of whether the sidebar was hidden in that tab, it pops back up (for all tabs).
I don't use vertical tabs, but I think what Rika is saying is that this might've been caused by combining the sidebars. When using vertical tabs, the sidebar should always be visible, regardless of start page or not. This is different behavior than when using default tab style though.