與 `\useshortskip` 的 `cases` 間距太短

Question

這是一個背頁 MWE。

範例中的程式碼：

\documentclass{book}

\usepackage{indentfirst}

\usepackage{nccmath}    % align & gather doesn't use shortskip: https://tex.stackexchange.com/a/386266/206774
\useshortskip           % nccmath seems to fix that even without this line


\begin{document}

1st case case case case case case case case 

\[\begin{cases}
    D: \text{wheel diameter} \\
    A = l \sin{\beta_1} \\
\end{cases}\]

2nd case case case case case case case case 

\[\begin{cases}
    D: \text{wheel diameter} \\
    A = l \sin{\beta_1} \\
\end{cases}\]

\end{document}

這就是問題：

看來只有第一個cases受影響。