We had the problem that the following commands both lead to the file not being untared after uploading:

tar -c folderx | dync -n folderx.tar -k untar:false data.qbic.uni-tuebingen.de
tar -c folderx | dync -n folderx.tar -k untar:true data.qbic.uni-tuebingen.de

This one worked:

tar -c folderx | dync -n folderx.tar -k untar:True data.qbic.uni-tuebingen.de

Users should either get feedback if their command is not accepted or the untar command (and I assume other similar commands) should ignore the case of letters.