The /locate command will, in certain situations, return a coordinate for a structure of the type you asked for, but it will not be the closest structure of that type. The locate command does not take the Y coordinate into consideration, so the entire Minecraft world can be divided into four quadrants, Q1(X +Z), Q2(-X Z), Q3(-X -Z), and Q4(+X -Z). The quadrant the player is in affects the coordinates that /locate will give the player.

Step by step process to test this

1. Load up the seed 5846045124490899663 and teleport to 0 70 0.
2. Use the command /locate Village in each of the 4 quadrants. In Q1 the  XZ coords given will be 864, -512. In Q2 and Q3 the coords given will be -880, 80. In Q4 the coords given will be 208, -800.
3. Use the command /locate Stronghold in each of the 4 quadrants. All 4 will give the same coordinates, -1320, -280.
4. Use the command /locate Shipwreck in each of the 4 quadrants. In Q1 the coords will be 0, 64. In Q2 the coords will be -192, 64. In Q3 the coords given will be -160, -176. In Q4 the coords given will be -256, -448.
5. Go to the Nether and teleport to 0, 40, 0.
6. Use the command /locate Fortress in each of the 4 quadrants. In Q1 the coords will be 128, -112. In Q2 Q3 and Q4 the coords will be -112, -144.

I have tested this in 2 different seeds so far. In theory, this bug will occur in any world. Based off the results above it appears that somehow the quadrant the player is in influences the behavior of /locate, but since several quadrants returned the same coords, or all of them in the case of the Stronghold, it is unclear how exactly this works.

This bug was tested in single player creative mode, but in theory would work the same in multiplayer or in different gamemodes like survival.