You can change that in the settings. It's under 'Tabs' in the 'General' section of 'Settings' from the hamburger menu in the top-right (check/uncheck "Enable Container Tabs").
The extra security aspect seems important, but the browser shouldn't just drop the user's previous history (for that tab) just because it's isolating things. :/
Hopefully this is just a case of "early stage feature" and bugs like this will be fixed. :)
Hopefully this is just a case of "early stage feature" and bugs like this will be fixed. :)