[galaxy-user] version_command tag problem

Hi everybody, I'm trying to add the version_command tag to my tools' xml files, but I run into a problem here. Currently I have: <version_command interpreter="python3">aln.py --version</version_command> in my xml. When I run the tool Galaxy tells me that it executed this: python3 /home/me/galaxy-dist/tools/modmapmin/aln.py --version &> /home/me/galaxy-dist/database/tmp/GALAXY_VERSION_STRING_1035 but when I check that temporary file it's empty (and so is the tool version line at the end of the run). This is puzzling because when I run that exact command line from my terminal, it writes 0.8.2 to the file just as it should. Any ideas what goes wrong here? Thanks and best wishes, Wolfgang