Attached test case. In the test case there is a blue box, which is the shadow host. Inside that box is a shadow DOM box with a black border. Clicking on the shadow DOM box will trigger it's :active state, which turns it green. Inside the shadow DOM box, there is a non-shadow span with a text node saying "Text". The bug is that when clicking on the text, the active state of the shadow DOM box will not get triggered. It seems that the active state is not reaching into the shadow DOM from the content node.

William, can you help a brother out?

So the issue here is similar to bug 1145910, except that instead of failing to propagate event state from shadow DOM to the light DOM, we don't propagate the state from light DOM into the shadow root where the nodes are distributed. The first case is actually specified (shadow DOM -> light DOM), but the other way is not. It looks like Chrome is propagating the state into the shadow DOM.