I am not a lawyer, and these comments do not constitute legal opinion, my own, my employer's, or any others'.
This post is not related directly and makes no comment on other timely happenings. I'm just following a train of thought.
I find myself wondering at the intersection of 'derived work' and 'residual knowledge'. SFAIK, on changing employment the future use of residual knowledge (eg. skills, not proprietary facts) is protected in at least some jurisdictions. LGPL source (to pick an example not precisely at random) is proprietary in the sense that there is an owner, and used under license.
But does 'derivation' require that the source be in front of you? Or that you are remembering the original source? Or thinking about it? Surely once you get to the point that your are remembering that laying out a solution using some pattern is useful, that is only residual knowledge, even if you conceptualised that pattern through looking at or hearing about some source.
Supposing residual knowledge rules could apply, and if only *some* jurisdictions protect residual knowledge, this could lead to a truly unpleasant situation in which *where* the code is typed becomes important. Blech!
The application of residual knowledge law in cases in which there isn't an employment contract is best left to those with more fortitude than myself.