During package installation: Gtk-CRITICAL **: file gtkwidget.c: line 1584 (gtk_widget_map): assertion 'GTK_WIDGET_VISIBLE (widget) == TRUE' failed. X stopped and the installer rebooted, at which point I caught this message. I don't know if it was the cause.
The message that you are seeing is definitely not the reason that X stopped and the machine rebooted. This is a message that pops up on just about every install and the guys are trying to determine what is causing the assertion failure. Post further information is X is still failing for you.
It isn't. I couldn't get it to happen again.
These messages are now gone from the installer in the latest cut of the tree (that is the cut after beta3)