How to use OpenBabel's --unique option in KNIME

Hello guys,

The standalone version of OpenBabel offers the possibility to filter duplicate molecules by using --unique option. When I tried to use it in KNIME bundled version of OpenBabel nothing happened. Other options (e.g. for adding/deleting hydrogens, for generating 2D/3D structure, etc.) are working without any problems.

What could be the reason? How can I use this feature in OpenBabel in KNIME?