They are. Libertarian is absolutely about property rights, and some of the biggest beefs libertarians have with our government is the extent to which it infringes on those rights.
I do have strong libertarian (little "l") leanings, which is one reason why I respect the rights of copyright holders to release their software under the license of their choice. Of course, that sometimes conflicts with other rights, such as freedom of speech in the case of some proprietary licenses (such as some from Microsoft), so in those cases I will complain. It's not some fuzzy "The leftists are coming, the leftists are coming," but an actual restriction on freedom of speech in order to control what's known about their software.
Of course I know you've been avoiding that latter issue, since you don't want to be seen condemning Microsoft for their unethical acts.
No! "It's the copyleftists are coming, the copyleftists are coming!"
I'll be happy to condemn Microsoft where appropriate, and they have certainly paid a heavy price in various courts for their misdeeds. But you always want to use them to distract from the discussion at hand, and protect your favorite leftists like Stallman on threads like this that have nothing to do with Microsoft to begin with.
Funny, wonder why when I just searched Yahoo for "Libertarian property rights" this was the second thing that came up, from libertariannation.org?