The other day, I encountered a strange error while trying to unshelve some work in TFS. For those of you who may not be familiar with it, TFS is one of the more server-oriented source control systems around. To keep work that you want, but that is not ready for checkin, you shelve it--which amounts to a semi-private checkin that is not on the main branch. Viewers can see and share one anothers' shelves.
In this case, I had started some major changes that would not be working for a demo, but some other changes were needed for the demo. The new changes included adding a variety of files, besides many modifications. So, I shelved it.
A few weeks later, I tried to unshelve it. I assumed that I would just have to merge the changes together (not a big deal, in this case). Instead, TFS complained that all of the new files still existed in the folder. The first TFS frustration. By default, when files are deleted from the project and from the source repository, TFS leaves them on disk. This would be sensible enough, if they at least handled it correctly in situations like this.
So, I decided to move all of the files to another location (instead of deleting them--time has made me paranoid about things like this). I reran the command. TFS still insisted that the files existed. Frustration #2. The files simply did not exist, yet TFS insisted that they did.
The long and short of it is that I had to take the files that TFS left on disk and manually readd and merge them into the project, as TFS simply would not allow the work to be unshelved.
It turns out that there is a known bug in TFS shelves, that occurs when files are added, then shelved, and then unshelved again. As a bug, this is so severe I don't know how TFS ever got released in this state, especially since using shelving in this manner is precisely the sort of thing that Microsoft recommends.