I'm using three activities for my desktop workflows and I find them rather useful... until I have to logout.
After logging back in, I have my previous session restored with all application windows matched to randomly selected activities.
Is this a known issue?

Moreover, the lack of the ability to send multiple grouped windows to their original activities (like it is possible to do for virtual desktops with "Move To Desktop" from the grouped application icon in the taskbar) renders the Activities experience somewhat clumsy, but maybe this fits in the wishlist category.