¿Cómo configurar el mapa mental en tikzposter? La figura en el medio no se muestra correctamente.

Question

\documentclass[25pt, a0paper, portrait]{tikzposter}  
\usepackage[utf8]{inputenc}  
 \title{Tikz Poster Example}  
\author{ShareLaTeX Team}  
\date{\today}  
\institute{ShareLaTeX Institute}  
\usepackage{blindtext}  
\usepackage{comment}  
\usepackage{tikz}  
\usetikzlibrary{mindmap}  
\usepackage{metalogo}  
\usepackage{dtklogos}  
\usetheme{Desert}   
\begin{document}  
\maketitle  
\block{~}  
{  
    \blindtext  
}  
\begin{columns}  
    \column{0.5}  
    \block{More text}  
{\begin{tikzpicture}  
  \path [  
    mindmap,  
    text = white, align=flush center,  
    level 1 concept/.append style =  
      {font=\large\bfseries, level distance = 4.5cm, sibling angle=90},  
    level 2 concept/.append style =  
      {font=\normalsize\bfseries, level distance = 3.3cm, sibling angle=50},  
    level 3 concept/.append style =  
      {font=\small\bfseries, level distance = 3.5cm, sibling angle=75},  
    tex/.style     = {concept, ball color=black,  
      font=\huge\bfseries},  
    engines/.style = {concept, ball color=green!50!black},  
    formats/.style = {concept, ball color=blue!50!black},  
    systems/.style = {concept, ball color=red!80!black},  
    editors/.style = {concept, ball color=orange!90!black}  
  ]  
  node [tex] {Samples} [clockwise from=0]  
    child[concept color=green!50!black, nodes={engines}] {  
      node [circle,draw,minimum size=6em,text width=7em]{\Large\bfseries  {Mixtures}}[clockwise from=0]  
        child { node [circle,draw,minimum size=6em,text width=5em]  {\large\bfseries{Series 1}}[clockwise from=131]  
                child { node[circle,draw,minimum size=7em,text   width=7em] {\large\bfseries{DNA Conc.}} }  
                child { node[circle,draw,minimum size=7em,text width=8em] {\large\bfseries{Degradation}}}  
                child { node[circle,draw,minimum size=7em,text width=7em] {\large\bfseries{Sensitivity}}}}  
        child { node [circle,draw,minimum size=6em,text width=5em]  {\large\bfseries{Series 2}}[clockwise from=340]  
                child { node[circle,draw,minimum size=6em,text width=8em] {\large\bfseries{Proportions}} }  
                child { node[circle,draw,minimum size=6em,text width=8em] {\large\bfseries{No. of Contributors}} }  
                child { node[circle,draw,minimum size=5em,text width=7em] {\large\bfseries{Shared Alleles}} } }  
}
    child [concept color=blue, nodes={formats}] {  
      node {Case Types} [clockwise from=270]  
        child { node[circle,draw,minimum size=6em,text width=6em]   {\large\bfseries{40 Mixtures}} }}  
    child [concept color=red, nodes={systems}] {  
      node [circle,draw,minimum size=6em,text width=6em]{\Large\bfseries{Single source}} [clockwise from=240]  
    child { node [circle,draw,minimum size=6em,text width=5em]  {\large\bfseries{5 Samples}}[clockwise from=180]  
    child { node[circle,draw,minimum size=7em,text width=7em]   {\large\bfseries{LR Check}} }}  
    child { node [circle,draw,minimum size=6em,text width=5em]  {\large\bfseries{7 Samples}}[clockwise from=180]  
    child { node[circle,draw,minimum size=7em,text width=7em]   {\large\bfseries{DNA Conc.}} }}  
        child { node [circle,draw,minimum size=6em,text width=5em]  {\large\bfseries{7 Samples}} [clockwise from=180]  
          child { node[circle,draw,minimum size=7em,text width=7em]   {\large\bfseries{Saturation}} }}  
        child { node[circle,draw,minimum size=6em,text width=6em]  {\Large\bfseries{94 Samples}} [clockwise from=135]  
          child { node[circle,draw,minimum size=6em,text width=5em]   {\large\bfseries{Stutter Ratio}} }  
child { node[circle,draw,minimum size=6em,text width=6em] {\large\bfseries{Variances}} }}}  
    child [concept color=orange, nodes={editors}] {  
      node {STRmix} };  
\end{tikzpicture}}  

    \column{0.5}
    \block{Something else}{Here, \blindtext \vspace{4cm}}
    \note[
        targetoffsetx=-9cm, 
        targetoffsety=-6.5cm, 
        width=0.4\linewidth  
        ]  
        {e-mail \texttt{[email protected]}}  
\end{columns}  
\begin{columns}  
    \column{0.5}  
    \block{A figure}  
    {   
            {\blindtext}       
    }  
    \column{0.5}  
    \block{Description of the figure}{\blindtext}  
\end{columns}  
\end{document}