# Cannot remove displayskips in beamer

The space that appears in the PDF above and below my align* environment is way to large. According to Remove vertical space around align, one of the two commented-out lines should remove it (at least the above space) but they change nothing.

1. How can I remove the unwanted space, preferably globally?
2. Why is this space so big? Is this a bug or a feature?

MWE:

\documentclass{beamer}
\usepackage{mathtools}
\newtheorem{question}{Question}

\DeclareMathOperator{\argmax}{arg\,max}
\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}

\begin{document}

\begin{frame}{Vector offsets}
We assume that a linguistic relationship between two words corresponds to a constant, cosine distance based offset.
\begin{question}[Syntactic test]
$a\:b\ c\:\_$?
\end{question}
%\setlength\abovedisplayskip{0pt}\setlength\abovedisplayshortskip{0pt}
\begin{align*}
y   &= x_b-x_a+x_c \\
d^* &= \argmax_d \frac{x_dy}{\norm{x_d}\norm{y}}
\end{align*}
%
\begin{question}[Semantic test]
How valid is $a\:b\ c\:d$?
\end{question}
\end{frame}
\end{document}


Workaround:

\documentclass{beamer}
\usepackage{mathtools}
\newtheorem{question}{Question}

\usepackage{etoolbox}
\newcommand{\zerodisplayskips}{%
\setlength{\abovedisplayskip}{0pt}
\setlength{\belowdisplayskip}{0pt}
\setlength{\abovedisplayshortskip}{0pt}
\setlength{\belowdisplayshortskip}{0pt}}
\appto{\normalsize}{\zerodisplayskips}
\appto{\small}{\zerodisplayskips}
\appto{\footnotesize}{\zerodisplayskips}

\DeclareMathOperator{\argmax}{arg\,max}
\DeclarePairedDelimiter{\norm}{\lVert}{\rVert}

\begin{document}

\begin{frame}{Vector offsets}
We assume that a linguistic relationship between two words corresponds to a constant, cosine distance based offset.
\begin{question}[Syntactic test]
$a\:b\ c\:\_$?
\end{question}
\nointerlineskip
\begin{align*}
y   &= x_b-x_a+x_c \\
d^* &= \argmax_d \frac{x_dy}{\norm{x_d}\norm{y}}
\end{align*}
How valid is $a\:b\ c\:d$?