• Minecraft Version: 1.12.2
• Forge Version: 14.23.5.2847
• BuildCraft Version: buildcraft-all-7.99.24.5
• IndustrialCraft Version: industrialcraft-2-2.8.176-ex112

Steps to reproduce the behavior:

1. Create a diamond pipe.
2. Attach two cobblestone pipes for output.
3. Attach some pipe for input.
4. In diamond pipe filters, set "Copper Cable" for the first pipe, and "Insulated Copper Cable" for the second.
5. Pass multiple cables into the diamond pipe.

Expected: The "Copper Cable" must go out from the first pipe, and the "Insulated Copper Cable" - from the second pipe.
Actual: The items choose pipes randomly.

This also works with "Tin Cable".