Hm.... maybe I'm doing something wrong, but that doesn't bring me the dotted lines back.
I create a gmask (auto tangent on, so that I have dotted lines). Then I hit Space+B, click the vertice, and the tangents 'disappear'. In break-mode, I click and hold the vertice and drag out, to extend the tangents again (they are now a solid line). As soon as let go of the tangent, and go back to move mode, I now move the left tangent separate from the right. And now I'm not able to get the dotted lines back....