It appears that [delphi] has no tag wiki. Since I have invested some time into it, I know there once was one.
I just read about the new tag wiki revision history and clicked through to see whether the tag wiki was still available in a revision. But what did I find?
Everything was still there. It seems that the recognition algorithm does not find the wiki text any more after the change was made to revisions.
Well this is by-design.
The tag wikis are upgraded on the fly, you can see the full list of wikis that were upgraded here: https://meta.stackoverflow.com/tags/tag-wikis
First time anyone visits the a wiki that was not upgraded to the new "post" format (which gives you the nice history and so on) it will upgrade the wiki.
Its a one time operation so its not really worth fixing.
This has since been fixed - maybe just a matter of releases. But now it looks as it should again:
