Ok, steps to reproduce:
1. Install the latest Forge release for Minecraft 1.11.2 ( 13.20.0.2228 ).
2. Make sure you don't have any mod in the mods folder.
3. Start a new default game.
4. By default you'll spawn near the x:0, z:0 coordinates, but not exactly there (maybe it will be something like x:120, z:-210).
5. Type /gamerule spawnRadius 5000.
6. Kill your character (either by typing the command /kill your_nick, or drowning yourself, or jumping off a cliff).
7. After respawning, press F3 and look at the coordinates. Now you are on negative x and z coordinates (it may be something like x:-4120 z:-3565) That means always northwest of the world spawn.
8. Kill your character again. And so on.