Wikimedia Bugzilla is closed!

MW Version: 1.23.1
Math Version: git master 084718af14d8597092337759b1b3ad95ec5be53f (current)
Server: Debian wheezy

What i did:
<pre>
cd wiki_path/extensions/
git clone https://gerrit.wikimedia.org/r/p/mediawiki/extensions/Math.git

cd wiki_path/extensions/Math/texvcheck
make

cd wiki_path/extensions/Math/math
make

vim wiki_path/LocalSettings.php
# Math
# http://www.mediawiki.org/wiki/Extension:Math
require_once "$IP/extensions/Math/Math.php";
$wgMathDisableTexFilter = true;
// ensure MW_MATH_MATHML; is added to the $wgMathValidModes array;
$wgMathValidModes[] = MW_MATH_MATHML;

// Set Mathoid as default rendering option;
$wgDefaultUserOptions['math'] = MW_MATH_MATHML;
$wgMathValidModes[] = MW_MATH_LATEXML; // adding LaTeXML as rendering option

// Set LaTeXML as default rendering option;
$wgDefaultUserOptions['math'] = MW_MATH_LATEXML;

$wgDebugLogFile = "/tmp/wiki.log";
//EOF

php wiki_path/maintenance/update.php --quick
</pre>

What i got:
* formula is working with MathML
* formula is working with SVG fallback
* formula is not working with PNG fallback

The fallback link for PNG is pointing to "index.php?title=Spezial:MathShowImage&hash=903286ede01eb3c73938de7eb75fb295&mode=0".
This page is showing the error message "Fehler beim Parsen (PNG-Konvertierung fehlgeschlagen. Bitte die korrekte Installation von LaTeX und dvipng überprüfen (oder dvips + gs + convert)): \int\limits_a^x f(\frac{\alpha}{2}\,)\,dxx".
The log file contains:
<pre>
Start request GET /index.php?title=Spezial:MathShowImage&hash=903286ede01eb3c73938de7eb75fb295&mode=                   0
HTTP HEADERS:
HOST: example.com
USER-AGENT: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0
ACCEPT: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
ACCEPT-LANGUAGE: de,en-US;q=0.7,en;q=0.3
ACCEPT-ENCODING: gzip, deflate
COOKIE: xyz_wikiUserName=username; xyz_wikiUserID=1; xyz_wikiToken=801a8770d53e5b929e427efb13abbf0c; xyz_wiki_session=kdgr2o6r4eqaen24cnt7o1g3i2; s5slide=4%3A3
CONNECTION: keep-alive
CACHE-CONTROL: max-age=0
[caches] main: APCBagOStuff, message: APCBagOStuff, parser: APCBagOStuff
[caches] LocalisationCache: using store LCStoreDB
Connected to database 0 at localhost
Fully initialised
User: got user 1 from cache
User: loading options for user 1 from override cache.
User: logged in from session
[Math] start rendering $\int\limits_a^x f(\frac{\alpha}{2}\,)\,dxx$ in mode 0
[Math] TeX: /var/www/xyz-wiki/htdocs/mediawiki-1.23.2/extensions/Math/math/texvc '/tmp' '/tmp' '\int\limits_a^x f(\frac{\alpha}{2}\,)\,dxx' 'UTF-8' 'transparent'
[texvc] Executing '/var/www/xyz-wiki/htdocs/mediawiki-1.23.2/extensions/Math/math/texvc '/tmp' '/tmp' '\int\limits_a^x f(\frac{\alpha}{2}\,)\,dxx' 'UTF-8' 'transparent''.
wfShellExec: /bin/bash '/var/www/xyz-wiki/htdocs/mediawiki-1.23.2/includes/limit.sh' '/var/www/xyz-wiki/htdocs/mediawiki-1.23.2/extensions/Math/math/texvc '\''/tmp'\'' '\''/tmp'\'' '\''\int\limits_a^x f(\frac{\alpha}{2}\,)\,dxx'\'' '\''UTF-8'\'' '\''transparent'\''' 'MW_INCLUDE_STDERR=;MW_CPU_LIMIT=180; MW_CGROUP='\'''\''; MW_MEM_LIMIT=307200; MW_FILE_SIZE_LIMIT=102400; MW_WALL_CLOCK_LIMIT=180; MW_USE_LOG_PIPE=yes'
[Math] TeX output:
 +15c8be621d90f691eb449a4699e14e87-
---
MessageCache::load: Loading de... got from global cache
LoadBalancer::reuseConnection: this connection was not opened as a foreign connection
Request ended normally
#EOF

ls -al /tmp/ | grep tex
-rw-r--r--  1 xyz-wiki xyz-wiki  172 Aug 18 14:45 17724_15c8be621d90f691eb449a4699e14e87.tex

/bin/bash '/var/www/xyz-wiki/htdocs/mediawiki-1.23.2/includes/limit.sh' '/var/www/xyz-wiki/htdocs/mediawiki-1.23.2/extensions/Math/math/texvc '\''/tmp'\'' '\''/tmp'\'' '\''\int\limits_a^x f(\frac{\alpha}{2}\,)\,dxx'\'' '\''UTF-8'\'' '\''transparent'\''' 'MW_INCLUDE_STDERR=;MW_CPU_LIMIT=180; MW_CGROUP='\'''\''; MW_MEM_LIMIT=307200; MW_FILE_SIZE_LIMIT=102400; MW_WALL_CLOCK_LIMIT=180; MW_USE_LOG_PIPE=yes'

ls -al /tmp/ | grep tex
-rw-r--r--  1 xyz-wiki xyz-wiki  172 Aug 18 14:45 17724_15c8be621d90f691eb449a4699e14e87.tex
-rw-r--r--  1 xyz-wiki xyz-wiki  898 Aug 18 14:55 15c8be621d90f691eb449a4699e14e87.png
</pre>

Why is the png file only created when i run the command in the shell?
Why is the folder /tmp and not a folder inside the wiki_path?
Any idea why no PNGs are created via the Webserver?