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).

Comments

Thank you for signaling this I was not aware of it. I'll install Theme Developper to check the issue. It is also for that kind of situation that sweaver include the toolbar plugin. This one add a link on the admin toolbar to display or hide Sweaver. However the toolbar module has no hook for that, so it require a specific hard code manipulation.