It's not quite a violation beyond the definition of the word, because the copyright holder isn't enforcing the GPL. Let me give you some background.
When we first put a system in place to hold democratic moderator elections, OpenSTV was actively distributed under the terms of the GPL (v2 or later). Anyone could use it, provided that they complied with the terms of the GPL should they distribute it.
OpenSTV also had a standing request that if institutional use was the intended use case that the agency conducting the election consider a donation to its development. We did that, because it was the right thing to do, which got us their permission (even though we didn't technically need it, because of the GPL) to distribute the software to our users.
None of that changed, but they've subsequently taken down the source code, which leaves us in this rather awkward place. The simplest solution at this point is taking the GPL out of the mix altogether, or possibly just relying on the web service that they provide. We'll get in touch with them. Even though no one is going to get mad and sue anyone, I don't like that we're not able to technically comply with the terms of the GPL, I'd rather just see if they can provide us with a simpler free-to-use-for-your-users kinda thing, or help us just automate everything over to their web service.
Edit (for clarity)
We were given the ability to distribute the 'compiled' version of OpenSTV by the authors, specifically for the manner that we intended to distribute it. What we didn't get at the time was any other license, and the only license that existed out in the public for the project was the GPL.
We had their direct permission to distribute the software in the manner that we were, in the manner that they wanted us to do it. The fact that they later stopped making the source code available is another matter, but one that is easily transposed on our situation. What we should have asked for was a much more deliberate dual license for our use, but no one thought that the project would be anything but GPL.
I think what we're going to end up doing is simply finding a way to push the results directly to their web service, as that's the simplest way.