Yes, certain properties cascade through the shadow boundary. That's completely intended, and easy to work around by using a shadow-scoped reset if you need to, but otherwise it's useful to be able to set the font or color for an entire tree-scope at once.
In all fairness, that's how a blank browser works by default (e.g. Times News Roman is the inherited font-family if you don't specify one) so is very likely the intended behavior.