If the value in a gtkTreeView is too wide for the display, calling scroll_to_cell() will cause the Tree View to start moving horizontally, which is not supposed to happen. I'm filing this against pygtk2 since that's what I'm using, but the bug could well be in gtk2. I'm attaching a sample program to demonstrate the behavior. Just start clicking the "clickme" button and see the tree start scrolling horizontally.
Created attachment 92040 [details] demonstration of scrolling bug
gtk bug.
Really looks like NOTABUG to me but assigning it Jonathan since he'll know for sure - you pass in a column and a horizontal align of 0.5: http://developer.gnome.org/doc/API/2.0/gtk/GtkTreeView.html#gtk-tree-view-scroll-to-cell says "If column is NULL, then no horizontal scrolling occurs", so if you don't want horizontal scrolling, then you should pass in 'None' instead of 'col'
The bug is that it keeps on scrolling to the left every time you click on the button.
Filed upstream as http://bugzilla.gnome.org/show_bug.cgi?id=142494 with some analysis.