Visited links (:visited) can't override a box-shadow defined with :link. I tried using !important, changing order of rules, nothing works. The worst part is you CAN define block attributes to the :link and :active links. (Let alone the specificity you all know is so weird)
It's difficult to confirm this bug without a test case. We don't believe there is an ongoing issue here. If you do feel there is a problem, please REOPEN this bug and include a test case illustrating the issue.