I see the problem with Firefox (12.0), not with Safari (5.0.2).
It appears for me only when the Theme developer (7.x-1.x-dev, 2012-06-05) module is enabled (its tickbox, unticked, is shown on the display in the same area as Sweaver).
In the Sweaver panel, on the Style, Borders & Spacing tab, the dropdown for Border style shows the choices, but does not allow a selection. Other changes in that tab seem to be effective without problem.
Perhaps Sweaver should not be combined with Theme developer (this is a documentation issue, not code).
Or perhaps it's a Theme developer issue (I don't know how to isolate one from the other).