Ensure consistent line height

source/beamerinnerthememetropolis.dtx

@@ -328,6 +328,9 @@
 \newlength{\metropolis@blocktitleadjustleft}
 \newlength{\metropolis@blocktitleadjustright}
 \newlength{\metropolis@blockbodyadjust}
+\providecommand{\metropolis@strut}{%
+  \vphantom{ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz()}%
+}
 \newcommand{\metropolis@block}[1]{
   \par\vskip\medskipamount
 %    \end{macrocode}
@@ -366,7 +369,9 @@
     leftskip=\metropolis@blocktitleadjustleft,
     rightskip=\metropolis@blocktitleadjustright]{block title#1}
       \usebeamerfont*{block title#1}%
+      \metropolis@strut%
       \insertblocktitle%
+      \metropolis@strut%
   \end{beamercolorbox}%
   \nointerlineskip%
   \usebeamerfont{block body#1}%

source/beamerouterthememetropolis.dtx

@@ -148,7 +148,7 @@
 %    Templates for the frame title, which is optionally underlined with a
 %    progress bar.
 %    \begin{macrocode}
-\newcommand{\metropolis@frametitlestrut}{
+\providecommand{\metropolis@strut}{%
   \vphantom{ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz()}%
 }
 \defbeamertemplate{frametitle}{plain}{%
@@ -157,7 +157,9 @@
       wd=\paperwidth,%
       sep=1.5ex,%
     ]{frametitle}%
-  \metropolis@frametitlestrut\insertframetitle\metropolis@frametitlestrut%
+  \metropolis@strut%
+  \insertframetitle%
+  \metropolis@strut%
   \end{beamercolorbox}%
 }
 %    \end{macrocode}