I am not sure if that really is an issue (and I guess the book has real numbers about it). I mostly think of the “Open Source Programmer at night” as a myth, or at least being the exception when speaking about Open Source Software that is actually being used by multiple parties in critical parts of their business systems.
Also in podcasts I sometimes hear programmers ranting about how tough their “life” and working conditions are at their day-to-day-job. Yet, the demand is very high and the salary is … “competitive” - as a developer you should be able to pick your job (if you can live with the 40h etc convention)! If you want to do Open Source, tell your company.
If I encounter some issue with Free (as in freedom, ~ Open Source) software, I will contribute, in the form of an creating a issue in the ticket-system (that is how developers keep track of what maybe has to be done), getting involved in the Forum, Mailing List or Chat, or propose an improvement (“Pull Request”). Many times this is about a clarification in the installation or maintenance instructions. I do this in my paid time (I bill my customers for it) and I believe any User should feel as an empowered user and just do the same - for me its part of the game. If my bosses (I dont really have any…) were to tell me: “Nope, you have to keep your improvements private” or “Sorry, thats something you have to do in your free time”, they’d disqualify as bosses. Just move on - there should be plenty of alternatives out there.