This is how the Bukkit disaster happened. Microsoft "bought" the leading Minecraft server software, hiring some of the major developers and I guess not telling anyone else, and some of them were unamused that they were (in their eyes) doing free work for Microsoft when their colleagues got hired. So they rescinded their GPL licensing of their contributions and sent DMCA notices. Which pretty much ended the project, except for Spigot continuing development in the form of patches that the server operator applies with a script.
It should be noted that the authors didn't rescind any licenses, per se. Rather, distributing binary versions of Bukkit was always in violation of the GPL (since the bundled Mincraft code did not have source available). The former author simply started enforcing this. Important distinction since rescinding the license would be a far more legally/ethically dubious action.
The license covers the code, not the trademark. You can use the code/software as long as you observe the license, you can use the trademark as long as you follow the rules set out by the trademark owner. E.g. you can totally use the code to make your own audio editor and distribute it, but the trademark terms might not allow you to call it "Audacity".
Copyright law and trademark law are different topics and have different ruling. Most software licenses (except 4 clause BSD or PHP License and few others) don't make any claims about names.
One might try to argue that a name used in software code and distributed under some open source license also gives rights to the name by being source ... but to my knowledge there are no court decisions.
Trademarks are actually still useful for open-source software, since they ensure that a malicious or incompetent party can't ruin the name of your software by shipping a modification that does bad things.
Jason Rohrer ran into this very issue when other developers made their own client for his game, using a variation on the game's name. They didn't respond to him asking that they don't use the name, and eventually he was convinced that trademarking the name is the right tool to project it. The original game client is still open-source (and maybe the server too, dunno).
GPL isn't "do whatever you want". It's "do whatever you want, as long as you let future users do whatever they want". That's what makes it such a good licence for the community.
Well, imagining it from the buyer's perspective, if I bought Audacity then now I can make changes to it and while there may be other forks, these changes will be likely be recognized as "the" Audacity.
So if for example I wanted to cross-promote my other products or add a "pro" paid version of some sort, I could do that, and those would end up in the main version most people are downloading.