This software bug is not new in any way.
It has been reported over and over again and is obviously very annoying. In fact, I'm not even sure if it is ONLY in Adobe but the dictionary support in adobe is generally pretty bad.
However, since I know you've been using djvu files: The dictionary in djvu files works excellent. However, I probably wouldn't go the long way and convert my pdf files to djvu files just to have dictionary support