I cannot verify the first case about removing the last tab also removes the toolbar, I assume by toolbar is the section that has the names of the tabs with the close button for each one. I tried with workspace and system browser in Pharo 4 and it works fine for me, I got the build just a few minutes ago. Reported this also in the issue tracker.
Keep in mind that everything is implemented 5 times. If you look at X, this might not be the same implementation of X. (in this case tabs).
And yes, the issue does a bad job in describing how to recreate the problem.
Does the slice get integrated to the pharo build even before the issue is checked as resolved ?
No.