A friend of mine ran into this issue but I recreated it to verify before I posted this - screenshot is of my own experience:
-Built a 'railed bridge'
-Placed railed bridge (screenshot shows it on land, but the effect is the same whether it's on land or over water)
-Proceeded to whack bridge until it disassembles
-Once the bridge's 'health' is depleted the game notes that a railed bridge has entered my inventory - but the origin bridge remains
-I proceed to attack the bridge, which is now at 0hp, and each hit generates a new railed bridge which enters my inventory
Result = infinite railed bridges!
Secondary result = infinite money through the saturation of the railed bridge market!