Stone bridge (if it is created in the map, in the map editor) - in the game - impossible to sell.
Windows 8.1 64 bit, 8 Gm RAM, Intel(R) Core(TM) I7-4500 CPU1.80 GHz 2.40
GHz GPU: AMD Radeon R7 M265, Intel(R) HD Graphics Family. Version game 1.40f9
Game Version:
Steam Public
Platform:
Windows
This is intended behavior.
these Bridges are in fact not stone bridges but Granite Bridges. In game they are intended for creating permanent themed walkways to make a map look like the campaign maps.
if you think this should be changed i would ask yo to make a post in the SG suggestion forum here:
https://forum.subterraneangames.com/forums/suggestions.10/
if you would ask for a toggle you would have my support but sadly im not in a position to change this alone