"Continue from last time" doesn't save fast enough

I have one of my mouse thumb buttons mapped to Alt+F4 to quickly close windows. In the case of Opera, I have modified my keyboard shortcuts to map Alt+F4 to Close page, 1 (instead of Close window). This way, I can click my thumb button to close a tab, and when no tabs are left, it closes Opera. I have also set Opera to Continue from last time on startup. So, the issue I'm seeing is that if I quickly tap my thumb button to close all my pages then close Opera, when I start Opera back up, I see all the pages I had closed. Another way you can reproduce this is to open a bunch of tabs, right click on a tab and select Close All, hit Enter for Yes and quickly hit the window's close button. When you start Opera back up, all of the closed pages are still there. If you close all the pages, wait a few seconds, then close the window, when you start Opera back up, it will be empty as expected. It seems like there's a delay before the current session is saved. I'm experiencing this issue on Opera v11.52. I tried it on Opera v11.51 on a different machine and it works as expected, i.e. Opera opens with no pages loaded if I closed all the pages in the last session.

That delay is as far as i know on purpose and for performance reasons. Nevertheless i don't understand why they don't save all opened tabs on shutdown of Opera when continue from last time is enabled. I would have implemented it like that, but maybe they found that a huge number of opened tabs would then delay shutdown too much.