In regards to the "do the devs test anything" comment by the OP above:
Remember, they are a small team. They test what they can, but they also can't spend their entire time testing, or no new content would ever get completed. This is why they put the content to Test Center and ask players to check it out. This also isn't unique to UO, just about every game I can think of that has rotating content, also has a Test Server. Even WoW brought in players and raiding guilds to test new content before it was released and they had a huge QA department.
There is also a huge difference in testing something that you know how it is supposed to work vs testing something that you are unfamiliar with. The Devs can look at the content and go through a checklist of what is supposed to happen, and if it does, that may satisfy their initial tests. Players are unpredictable and will do things in ways no one could predict, and they will come up with tactics that may break the game, etc. This is why player testing in any game is important. I'm not speaking blindly on this either, I am a former lead QA tester for an unnamed video game company. No one can break a game like a player looking for an advantage in new content. The good testers are the ones that report these advantages and not just keep them for their own personal gain.
Test Center is open to all. Hop on when they release new content and give it a try for an hour. If you find something not working, they listen well on the official forums. But to fix something it has to be reproducible. "X happened, fix it!" with no other details really helps no one. Even if you do not know why something happened, giving details you may find meaningless could be the key to the Devs fixing the issue.
For what it's worth, I did tons of testing on TC this patch and was one of the people who did report the Plunderbeacon continuing to fire bug as well as the no crate drop bug. The problem is/was, it wasn't until it went live and enough people were doing the content, that we were able to piece together that proximity to a shore or server line was causing the issue (and even then it is not 100% consistent).
Even with that new information, how close is "close", it is still an unknown variable. I have had bugged beacons that were literally right next to the shore, and bugged beacons that were about 1 screen away from shore. But at the same time, I've had beacons that work fine somewhere in between that. I've had firing beacons that also dropped crates, but non-firing beacons that did not drop a crate. The problem also may not present itself if the Devs manually spawn a plunderbeacon near the shore, maybe it only happens with an RNG spawn that appears near the shore, who knows.
