The Thief 2 patch patches only the thief2 executable. It does not patch the editor. There may be some incompatibilities when using a mission generated in the previous version of the editor and trying to run on a later version of the main game program. A version of the editor concurrent with the patched game is available for download. If you have already set up the editor, simply replace the dromed.exe from the cd with this one: Dromed for use with Thief II v1.18
The patch also changed many of the missions. The unstripped missions provided with the original editor release do not reflect the changes made in the patch. The updated versions of the unstripped missions can also be downloaded. These should be used in place of the unstripped missions available with version 1.07.