> entrenching a preference for one style of licensing over another.

Sure, that's true. The intent of the law is to give a special carve-out for, in essence, Free and Open Source software. It seems clear that it was deliberately written so as not to include proprietary freeware, say.

> We all know what set of licenses the FOSS zealots would prefer for us to release code under, and those who release license-free or public domain software anyway typically do it with full knowledge of such arguments.

Like what? Really, it's very rare for code to be released into the public domain like this. I've never seen a compelling argument for doing so. If your intention is to make the code available to all, to do with as they wish, the legal reality is that the best way to achieve this is to release the software under a permissive licence, rather than releasing it to the public domain.

If the exemption really doesn't cover public domain software, that presumably means that, as the copyrights on Free and Open Source software eventually expire and they enter the public domain, they will no longer be exempt. Again though this isn't of practical concern.

edit Come to think of it, publicly available software developed by the US federal government is released into the public domain, right? There doesn't seem to be much software like this though.

Direct link to the text of the bill: https://legiscan.com/CA/text/AB1856/id/3456513