Patents doesn't mean "nobody is allowed to use it"; patents mean "you are required to license the patent from the patent-holder, which usually requires paying royalties."
I could totally see the point of a FOSS software project that implements a patented algorithm, where people work together to improve the thing but everyone who uses it still has to get a license from the patent-holder. (For a recently-top-of-mind example, Fraunhofer's MP3 decoding patent.)
Thus, it's not obvious that a FOSS license automatically implies patent release. Fraunhofer could have open-sourced some reference MP3 encoder themselves, without releasing the MP3 patents.
I think the situation you mention has a significant distinction: Fraunhofer (or whoever) would presumably advertise that they expect you to get a patent license to use the code in a product. Either they'd explicitly state that up front, or their lawyers would say it with the first politely worded letter to someone who starts using the "open source" code.
Software distributed under those terms would no longer adhere to OSI's definition of open source (I think it violates points 1, 3, and 6) nor the FSF's Free Software Definition (points 2 and 3).
It might not stand up in court, but I do think it's obviously unethical to release patent-encumbered "FOSS" without mentioning your patents and then demand users obtain a license after the fact.
> It might not stand up in court, but I do think it's obviously unethical to release patent-encumbered "FOSS" without mentioning your patents and then demand users obtain a license after the fact.
I would be amazed if something like this does not stand up in court. Read the BSD license — it's really relatively simple english.
I could totally see the point of a FOSS software project that implements a patented algorithm, where people work together to improve the thing but everyone who uses it still has to get a license from the patent-holder. (For a recently-top-of-mind example, Fraunhofer's MP3 decoding patent.)
Thus, it's not obvious that a FOSS license automatically implies patent release. Fraunhofer could have open-sourced some reference MP3 encoder themselves, without releasing the MP3 patents.