Replayer breaks when the first fullmove number is 10 or more

Question

First fullmove number is 2:

[FEN "rnbqkbnr/pppp1ppp/8/4p3/4P3/8/PPPP1PPP/RNBQKBNR w KQkq - 0 2"]

2. Nf3

First fullmove number is 10:

[FEN "rnbqkbnr/pppp1ppp/8/4p3/4P3/8/PPPP1PPP/RNBQKBNR w KQkq - 0 10"]

10. Nf3

AFAICT, both of these should show the replayer, but only the former does.