Try this...go to any folder and assuming you've deselected the option to send files to the Recycle Bin - delete any file. Now immediately hit the Undo button to backtrack deleting this file. The file does not return. It's gone for good.
I'm not sure if DOpus documentation is clear on this...but it seems the only way to restore any deleted files assuming you want this ability is to not uncheck the option of sending files to the Recycle Bin. This to me seems counter intuitive to the idea of being able to restore deleted files period. You should be able to recover data from tracks not already overridden by other data files. So why can't files be immediately recovered?
My guess is it's because Opus isn't written to do that. Years ago I used to have some specialized utilities that would attempt to recover files actually deleted (with only limited success by the way) but I quit using them once Windows introduced the recycle bin.
Not all operations can be undone. Some are permanent. Deleting a file, without using the recycle bin, is one of those operations. (Although you can, with varying degrees of success, often undelete files using special tools. They don't always work, though. Sometimes the data has simply been overwritten.)
If you want to be able to undo deletes then use the recycle bin. That's exactly what it's there for. There's nothing counter-intuitive about it.
[Edit: I must've been writing my reply at the same time as Tanis.]
I don't want this to sound cynical...but but it's clear to me this "feature" of restoring deleted files could be an add on feature GPSoftware could introduce anytime between now and the next major upgrade.
Such a feature like this would really set DOpus apart from the competition. I'm sure they've thought about it. The question is whether they'll decide to bring this feature in. After all, I'm sure there are horror stories about people accidentally deleting their important folders with files that were meant to be kept.
I had a horror story recently when I deleted the wrong folder (Recycle Bin option was checked at this juncture) and all the files were gone. I naively hit the undo button hoping this would magically bring back the files. No dice. If GPSoftware is generous enough to include the ability to secure delete files you don't want recovered into DOpus...then it's clear they could introduce a recovery feature to bring back deleted files.
Writing an undelete that works safely is very complicated and not guaranteed to work. It also has to be coded differently for each different filesystem. There are also plenty of existing tools to do the job if you lose some files, some of them free.
You make it sound like GPSoftware could throw the feature together in five minutes but in reality it would take a lot of time and effort to write and even more time and effort to test and prove robust. There is no API for undeleting files; it requires direct manipulation of the disk at low-levels of the FAT and NTFS filesystems (and any others it has to work with) which is unrelated to anything else Opus does/uses. It's quite a specialised task.
There's a reason that Opus, Explorer and every other file manager I can think of don't have this feature.
This undeleting issue reminds me of something. Microsoft had promised a new file system code named "WinFS". Is this already available for the 64 bit version of Vista for instance? Or maybe Windows 2008 Server?