Descriptive Problem Summary: In the map editor, after using Find and Replace to replace a full tile turf with a partial tile turf, covering the replaced partial tile turf with a full tile turf followed by using undo results in world.turf being added as an underlay to the partial tile turf.

Numbered Steps to Reproduce Problem:
1) Download the following test project: http://files.byondhome.com/Higoten/Tests/ Replace%20Undo%20issue.zip (Same project as ID:2836281)
2) Navigate to map.dmm. Note that the purple turf is set as world.turf.
3) Use Find and Replace to replace /turf/Test2 with /turf/Test3 (Use Replace All as Replace doesn’t work in this instance, detailed in ID:2836281).
4) Note that the black turfs have been replaced with blue 3 turfs, with no world.turf as an underlay.
5) Ensure that Insert mode is on. From the instance editor, select /turf/Test2.
6) Using the Pencil tool, cover one of the /turf/Test3.
7) Undo the last action (Ctrl + z).
8) Observe that world.turf has been added as an underlay to /turf/Test3.

Expected Results: For world.turf not to be added as an underlay.

Actual Results: World.turf is added as an underlay.

Does the problem occur:
Every time? Or how often? Every time.

When does the problem NOT occur? Unknown.


Other note: Having world.turf added as an underlay during the find/replace step of a full coverage turf with a partial coverage turf would seem to be desirable behavior, but the current find/replace behavior is on-par with the prior behavior of find/replace.