I'm not sure what you think is wrong. Compacting occurs across all the folders in TB, not just Trash and Junk. When an email is moved from one folder to another, it leaves behind blank space that cumulatively adds up. Compacting removes all this 'space'. If you click on the 3 dots to the right of +New Message and select 'Show Folder Size', you will be able to see the size of each data file relating to the folder. As you move files away from these, the size doesn't reduce because it crates 'blank space'. Compacting removes this.

frisée, thanks for your response. It is possible that I don't really understand the situation, but this is totally different that TB has acted for me in the past. Whenever I have emptied the Trash it has always taken a few moments to accomplish that. Then when I select Compact, it will take a few moments and show me the space recovered. Then when I go to the In Box and select Compact it takes a long time to work its way through my large file. So the recent behavior of instant emptying of Trash and no compaction, but getting compaction from my small Junk folder, does not make sense to me. Thanks.

I advised you about how to show the space being used on your HD by each of the folders. If you do this, you will see how much space is being used and whether it seems to be disproportionate to the emails contained.

If the space is not shown, it's 'zero'.

If you then compact a folder, you would see a size reduction *if* there is blank space to remove.

Perhaps make some blank space in one of the suspect folders and then see what happens when you compact it?