Sounds like whatever you tried to export was not a real html table but something that was constructed from 3 or more table elements, which is pretty stupid IMO. And sadly there is nothing i can do to stop webdevelpers from doing things like this.
The addon itself is perfectly capable of exporting real html tables (its basically what it was made for), as you can see in the demo video. If you are having trouble it is likely that whatever you are trying to export/copy is not as simple it might look. In this case, you might have more luck with an addon called "Table Capture" by the addon developer GeorgeMike. It's paid but it might be capable of dealing with non-trivial html tables. Hope this info helps.