TikZ word search diagram v2

As a continuation of TikZ word search diagram here is the problem I'm facing. I did what Explorer suggested and it worked fine except that my rounded rectangles look like sausages or like Hieroglyphic cartouches because at their narrow ends they have lines on the secondary axis:

Here is the code:

\documentclass{article}
\usepackage[cmyk]{xcolor}
\definecolor{myPB}{cmyk}{0.85,0.75,0,0}
\definecolor{myLB}{cmyk}{0.1,0.06,0,0}
\usepackage{tikz}
\usetikzlibrary{matrix,backgrounds}
\newlength{\mydrawlinewidth}
\setlength{\mydrawlinewidth}{1pt}
\NewDocumentCommand{\markA}{ O{red} m m }{%
    \draw[rounded corners=6mm,opacity=.5, line width=2pt,myPB,fill=myLB] 
    ([xshift=5pt,yshift=-5pt]yannis-#2.north west) 
    rectangle 
    ([xshift=-5pt,yshift=5pt]yannis-#3.south east);
}
\NewDocumentCommand{\markB}{ O{red} m m }{%
    \draw[rounded corners=6mm,opacity=.5,line width=2pt,myPB,fill=myLB]
       ([yshift=2pt]yannis-#2.north) 
    -- ([xshift=2pt]yannis-#3.east)
    -- ([yshift=-2pt]yannis-#3.south)
    -- ([xshift=-2pt]yannis-#2.west)
    -- cycle;
}
\NewDocumentCommand{\markC}{ O{red} m m }{%
    \draw[rounded corners=6mm,opacity=.5,line width=2pt,myPB,fill=myLB]
       ([xshift=2pt]yannis-#2.east) 
    -- ([yshift=-2pt]yannis-#3.south)
    -- ([xshift=-2pt]yannis-#3.west)
    -- ([yshift=2pt]yannis-#2.north)
    -- cycle;
}
\begin{document}
\begin{tikzpicture}
        \matrix (yannis) [%
            matrix of nodes,%
            column sep=0mm,%
            row sep=0mm,
            nodes={
                % draw,
                rectangle,anchor=center,
                line width=0.5pt,
                inner sep=2pt,outer sep=0pt,
                %font=\bfseries\huge,
                minimum size=1.1cm,
                }
            ]
      {
         S & G & A & Q & Q & T & C & E & F & R & E & P & Y & W & R \\
         W & L & Q & E & L & B & A & R & A & P & M & O & C & E & L \\
         Y & I & T & S & X & E & L & I & Y & A & H & U & W & R & A \\
         B & K & E & E & Y & C & W & L & J & T & M & A & K & B & F \\
         J & E & R & I & O & R & T & M & K & E & R & L & Q & E & T \\
         P & N & P & L & S & B & R & W & H & D & U & U & E & H & E \\
         E & E & R & R & E & W & V & S & S & M & L & N & K & E & R \\
         H & S & E & E & H & T & A & P & H & Y & S & I & C & A & L \\
         S & S & T & D & S & H & E & U & Q & V & L & V & R & Z & I \\
         O & R & N & N & I & F & L & L & A & S & N & E & E & K & F \\
         M & T & I & U & N & L & G & E & P & H & U & R & A & S & E \\
         W & K & O & Q & U & P & U & H & A & M & G & S & T & M & I \\
         A & F & A & R & P & J & M & S & L & R & O & E & E & H & C \\
         B & X & H & C & A & I & H & S & A & M & S & C & D & F & G \\
         I & P & R & O & P & H & E & T & S & N & S & I & F & X & Q \\
      };
    \begin{scope}[on background layer]
       \markA{1-6}{1-12}
       \markA{1-14}{6-14}
       \markC{1-15}{7-9}
       \markA{2-2}{9-2}
       \markA{2-4}{2-13}
       \markA{3-3}{11-3}
       \markA{3-4}{11-4}
       \markA{3-6}{3-12}
       \markA{3-15}{11-15}
       \markC{4-11}{9-6}
       \markA{6-5}{13-5}
       \markA{6-12}{13-12}
       \markA{7-1}{11-1}
       \markB{7-5}{14-12}
       \markA{8-8}{8-15}
       \markA{8-13}{14-13}
       \markB{10-7}{15-12}
       \markB{11-2}{15-6}
       \markA{14-3}{14-10}
       \markA{15-2}{15-9}
    \end{scope}
\end{tikzpicture}
\end{document}

How can I fix this?

@mickep I replaced the snippets by a complete minimal example.