I'm not saying that I have a case showing that "what you do on your own time is yours". That won't be the case, especially if you've signed an agreement to the contrary as a salaried employee.
I am simply pointing out that Cubic v Marty does not in any way disprove that idea that "what you do on your own time is you own" either, because that's not what happened in that case. Instead, the employee had an idea directly relevant to their employer's business, showed it to them, got a raise, pursued it as an actual work project, and then after all that went off to patent it privately. That is not really a situation that has to do with someone inventing something on their own in their private time having nothing to do with work, where the question is whether the employer should own it.
The decision in Cubic v Marty should not be surprising or remarkable from what I have read. As an employee, you obviously cannot take home technology ideas that you were pursuing at work, as an official work project, and expect to patent them and get away with it. If you think there is something specifically interesting and relevant about it, then please point that out since I'm not sure what I'm missing. I am not saying that I have a more relevant case, just that I don't follow the relevance of that one.
If you are a salaried employee, and you use company resources on the project, or review it with other employees, or the project is in your employer's field of business, or if you pursue the project as an official work project, and it's in the line of work you do for your employer, and if you have signed an agreement agreeing to do so, and these are all signs that the employer owns the result. The case where none of those things are true is the case that I think will be interesting.