absolute position changing in TikZ environments

absolute position changing in TikZ environments

I am working on slides in beamer with a modified version of the Torino
theme. When drawing with TikZ, the absolute positioning seems to not work
as expected. In particular, when I have two tikzpicture environments and I
reference back to the previous one from the latter, the coordinates are
off.
\begin{frame}
\begin{tikzpicture}[overlay, remember picture]
\drawhelp;
\coordinate (topcorner) at (0,0);
\coordinate (rightcorner) at (5,-2);
\coordinate (bottomcorner) at (3,-2);
\draw (topcorner) -- (rightcorner);
\end{tikzpicture}%
\begin{tikzpicture}[overlay, remember picture]
\draw (topcorner) -- (bottomcorner);
\end{tikzpicture}
\end{frame}
Specifically, the line in the second tikzpicture is drawn lower than it
should be, corresponding with the spacing for the paragraph between the
tikzpicture environments. The first line is drawn on (0,0) -- (5,-2)
whereas the second line more or less corresponds with (0.95,0) --
(3.95,-2). If there is no paragraph or newline between the environments,
then the problem does not occur.
Furthermore, the problem does not occur in a blank LaTeX document (i.e.
there does not appear to be anything at fault with the above code), nor
does it occur when I revert to the clean Torino theme. Apparently, some of
the alterations that I have made seem to have an effect on the absolute
positioning of TikZ. However, even after considerable effort, I am not
able to create a minimally working example. This makes it hard to pinpoint
whether some package, option, custom command ... is at fault. Hence my
question:
Which settings/packages/options/ ... might affect the absolute positioning
in TikZ from not working as expected? Any plausible causes? I seem to
remember having the very same problem a couple of years ago, though I fail
to remember whether the problem was ever resolved back then.