I have just tripped over a display issue when using frozen columns along with a toolbar.
To illustrate the problem please see the following dojo
If you run this example and hit the 'refresh' button the toolbar gets moved down by 1px causing the display of a 2px border at the top and the removal of the bottom border.
With the 'locked' attribute commented out the toolbar remains static.
Investigations show the problem looks to be caused be the injection of the 'k-load-mask' div.
Without frozen columns this div gets inserted after the 'k-grid-content' div, but with frozen columns the div gets inserted before the 'k-grid-toolbar' div causing the unsightly display issue.