sort -V or ls -v sort strange behavior

[Ice Ninja]

Hi Dev,

I cannot explain why a hyphen - can change the sorting order.

$ sort -V <<<'2.yamlmode
2.1.yamlmode
2.1.yaml-mode
2.yaml-mode'
2.yamlmode
2.1.yamlmode
2.1.yaml-mode
2.yaml-mode

I assume the following result is expected.
2.yamlmode
2.1.yamlmode
2.yaml-mode
2.1.yaml-mode

Is it a bug or are there rules I am not aware of.

Thanks.
Aeron Wang