Vertical space before align environment is smaller than before displayed math

Question

The result of the following code is strange: vertical space before align environment is smaller than displayed math. What is the problem with align environment?

Edit: I want the same vertical space before and after align environments, just like other displayed formulas.

\documentclass{article}

\usepackage[14pt]{extsizes}
\usepackage{amsmath}

\setlength{\lineskiplimit}{4pt}
\setlength{\lineskip}{4pt plus 1pt minus 1pt}

\AtBeginDocument{%
  \setlength{\baselineskip}{19pt plus 1pt minus 1pt}%
}

\begin{document}

\setlength{\fboxsep}{0pt}

\noindent
\fbox{\makebox[\textwidth]{lazy dog}}
\begin{align*}
  \boxed{f(x) = \sin x + 1}
\end{align*}
\fbox{\makebox[\textwidth]{lazy dog}}
$$\boxed{f(x) = \sin x + 1}$$
\fbox{\makebox[\textwidth]{lazy dog}}
\[\boxed{f(x) = \sin x + 1}\]
\fbox{\makebox[\textwidth]{lazy dog}}

\end{document}

Answer 1

According to @DavidCarlisle's comment, the problem could be fixed with

\normallineskiplimit=\lineskiplimit