I was thinking about using \pgf@marshal but that is actually a lot more tokens.

--- a/tex/generic/pgf/basiclayer/pgfcoretransformations.code.tex
+++ b/tex/generic/pgf/basiclayer/pgfcoretransformations.code.tex
@@ -466,6 +466,7 @@
 % }
 %
 \def\pgftransformlineattime#1#2#3{%
+  \pgfgettransformentries\pgf@tempaa\pgf@tempab\pgf@tempba\pgf@tempbb\pgf@notimportantx\pgf@notimportanty
   \pgf@process{#2}%
   \pgf@xb=\pgf@x% xb/yb = start point
   \pgf@yb=\pgf@y%
@@ -479,6 +480,20 @@
   \ifpgfslopedattime%
     \advance\pgf@xc by-\pgf@xb%
     \advance\pgf@yc by-\pgf@yb%
+    % Now that we get the tangent vector without transformation
+    % It suffices to apply the non-shift part of the transformation
+    \ifpgfresetnontranslationattime
+      \begingroup
+        \pgfsettransformentries\pgf@tempaa\pgf@tempab\pgf@tempba\pgf@tempbb{0pt}{0pt}%
+        \pgf@pos@transform{\pgf@xc}{\pgf@yc}%
+        \edef\pgf@marshal{%
+          \pgf@xc=\the\pgf@xc
+          \pgf@yc=\the\pgf@yc
+        }%
+      \expandafter\endgroup\pgf@marshal
+    \fi
+    % OK, now xc and yc are correctly tangent to the line
+    % Continue the usual routine
     \ifpgfallowupsidedownattime%
     \else%
       \ifdim\pgf@xc<0pt%

+1 to the use of \pgf@marshal. I was also thinking about providing a pair of \pgf-get-transform-@non-shifting and \pgf-set-transform-@non-shifting, so we could use

\pgfgettransform@nonshifting\pgf@temp
[...]
\expandafter\pgfsettransformentries\pgf@temp{0pt}{0pt}

with definition

\pgfgettransform@nonshifting#1{%
    \edef#1{{\pgf@pt@aa}{\pgf@pt@ab}{\pgf@pt@ba}{\pgf@pt@bb}}%
}

+1 to the use of \pgf@marshal. I was also thinking about providing a pair of \pgf-(get|set)-transform-@non-shifting, so we could use

\pgfgettransform@nonshifting\pgf@temp
[...]
\expandafter\pgfsettransformentries\pgf@temp{0pt}{0pt}

Example:

\begin{tikzpicture}[scale=1.35, transform shape]
      \node [shape=person, monitor, minimum size=5em] (h) {};
      \node [ellipse callout, callout absolute pointer = {(0,0)}, draw, above right = 1em and 0em of h, align=center] (co) {\raisebox{.2\height}{
        \begin{tikzpicture}
          \node [draw, alice] (a) {Alice};
          \node [draw, bob, right = of a] (b) {Bob};
          \node [draw, charlie, right = of b] (c) {Charlie};
          \node [draw, overlay, cloud callout, callout absolute pointer = {([yshift=.5em]a.north east)}, above = 1em of b] (x1) {x};
          \node [draw, overlay,cloud callout, callout absolute pointer = {([yshift=.5em]b.north)}, callout pointer segments = 1, above = 1em of b] (x2) {x};
          \node [draw, overlay, cloud callout, callout absolute pointer = {([yshift=.5em]c.north west)}, above = 1em of b] (x3) {x};
          \node [above = -2em of x1] (x1) {};
        \end{tikzpicture}}
      };
      \node [rectangle callout, callout absolute pointer = {([xshift=2.5em,yshift=-.5em]h.east)}, draw, above right = -2em and 4em of h] (f) {\(K_{Alice}x \land K_{Bob} x \land K_{Charlie} x\)};
      \node [rectangle callout, callout absolute pointer = {([xshift=2.5em,yshift=-.6em]h.east)}, draw, below = 1em of f, align=center] (p) {\(E_{\{Alice, Bob, Charlie\}} x\)};
      \node [rectangle callout, callout absolute pointer = {([xshift=2.5em,yshift=-.7em]h.east)}, draw, below = 1em of p, align=center] (p2) {\(C_{\{Alice, Bob, Charlie\}} x\)?};
    \end{tikzpicture}

In reply to @hmenke:matrix.org
muzimuzhi: Do I understand this correctly, that you already committed a fix for #1075? In this case, just close it with label closed-fixed. Maybe add a comment to the issue containing the hash of the commit. Don't worry about the commit message, accidents happen and if you look at the old commit imported from CVS you'll find lots of *** empty log message *** with thousands of lines of changes.