Both of these are because we have no reliable way of detecting when the bookmarks window closes. These will be release noted (whenever I get around to revising the release notes).
Okay, THAT is strange -- I have no idea how that could possibly happen. To make sure I understand you correctly: you used the Web menu entry, and Tear (the Browser Switchboard default browser) came up; then you closed Tear, opened the Web menu entry again, and the MicroB bookmarks window (without the about:blank window that Browser Switchboard opens) came up?
That looks like Browser Switchboard launched MicroB (otherwise the browser processes would show as "/usr/bin/browser"). I realize this might be difficult to reproduce, but can you try to reproduce it with browser-switchboard running in a terminal, and show the debug output?