In this case, it's a not a bug but a feature. The inner text box is decoupled from the fixed height setting for a number of reasons, e.g. lower box part support and breakability. Therefore, you cannot use \vfill, because the inner text box has no fixed height.
But, you can use a minipage with a fixed height inside the tcolorbox. You can put this minipage into the box setting options:
\documentclass[]{scrartcl}
\usepackage[many]{tcolorbox}
\newtcolorbox{bilety}
{ enhanced,
space to upper,
%height=5cm,
segmentation style={black, solid, opacity=0, line width=0pt},
colback = black!5!white,
colframe = black!15!white,
sharpish corners,
before upper={\begin{minipage}[t][4cm]{\linewidth}},
after upper={\end{minipage}},
}
\begin{document}
\begin{bilety}
some text
\par\vfill
some other text
\end{bilety}
\end{document}
Update (16-Nov-2018):
Alternatively, the option text fill can be used to automatically insert a minipage with adapted fixed height:
\documentclass[]{scrartcl}
\usepackage[many]{tcolorbox}
\newtcolorbox{bilety}
{ enhanced,
%space to upper,
height=5cm,
%segmentation style={black, solid, opacity=0, line width=0pt},
colback = black!5!white,
colframe = black!15!white,
sharpish corners,
text fill,
}
\begin{document}
\begin{bilety}
some text
\par\vfill
some other text
\end{bilety}
\end{document}
Load theorems library (I do it with class option most) and use ams or any other maths options.
ams set upper and lower parts to mathematical mode with \displaystyle. You don't need equation environments is these boxes. And you don't need valign.
\documentclass{beamer}
\usepackage[most]{tcolorbox}
\newtcolorbox{equationframe}{
math
}
\begin{document}
\begin{frame}
\begin{itemize}
\item[]
\begin{equationframe}
p(x,y)=\begin{cases}
\min\{q(x,y),\frac{\pi({y})q(y,{x})}{\pi(x)}\}, \quad x\neq y\\
1-\int_{x\neq y} p(x,y)
\end{cases}
\end{equationframe}
\begin{equationframe}
\pi(x)p(x,y)=\min\{\pi(x)q(x,y),\pi(y)q(y,x)\}=\pi(y)p(y,x)%
\end{equationframe}
\end{itemize}
\end{frame}
\end{document}
Update: ams equation*, ams align*:
Instead of math, tcolorbox also offers some other mathematical boxes: ams equation, ams align, ams gather, ...
\documentclass{beamer}
\usepackage[most]{tcolorbox}
\begin{document}
\begin{frame}
\begin{tcolorbox}[ams equation*]
p(x,y)=\begin{cases}
\min\{q(x,y),\frac{\pi({y})q(y,{x})}{\pi(x)}\}, \quad x\neq y\\
1-\int_{x\neq y} p(x,y)
\end{cases}
\end{tcolorbox}
\begin{tcolorbox}[ams nodisplayskip, ams align*]
\pi(x)p(x,y) & =\min\{\pi(x)q(x,y),\pi(y)q(y,x)\}\\
& =\pi(y)p(y,x)%
\end{tcolorbox}
\end{frame}
\end{document}
Best Answer
Two options; the first one uses a manual adjustment made using the
baselinekey for thetcolorboxes, and the second one uses the optionvalign=cfor an\adjustboxfrom theadjustboxpackage; the setting is done automatically usingbeforeandafter:The complete code with both possibilities: