[gp2000]

That isn't a bug. In the original if a guess contains a repeated letter and there is only one occurrence of that letter in the target work then the first (on the left) letter will be yellow and the second black.

You can see this with today's word by guessing MOTTO. The leftmost T will be yellow and the rightmost will be black.

Similarly, if you guess TENET the initial T is black but the final T is green.

Today's word is ZBVFG (rot13).

[esrauch]

I believe op was saying that the linked reimplementation incorrectly misses the behavior that you are describing.