'Deleted Items,' huh?

[w7]

My trash can is called Trash. It shows up as Trash in Thunderbird and Squirrel Mail. It also shows up as Trash in all my accounts except one. In the account concerned, a 'Deleted Items' folder shows instead. When I open Personal Settings/Folders, it still lists "Trash" as being subscribed, but it no longer shows in the tree pane.

What happened?