I don't know if this is a bug, but it certainly seems odd. Build markers for a lot of objects can be placed in locations in which the actual objects can not be placed in the editor.
Examples:
Mirrors and powder kegs can not be placed on pits, water, shallow water, master walls!, hold complete walls!, or (for some reason) crumbly walls or secret walls. Placing a build marked for one of these will result in the engineer building it. A keg or mirror on a pit, water, or shallow water tile will just hover there. You can even push it off into another tile that usually accepts that kind of object (such as floor).
Potions and orbs can also be placed on water or pit tiles using build markers, even though they can not be placed directly using the editor. They will not fall or sink, but will just sit there. You can even use a platform or raft to get to a potion hovering over a pit or water and make use of it.
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Links to neat forum tools that I always have trouble finding:
Click here to view the secret text
[Last edited by mrimer at 12-12-2015 05:52 AM]