Gray space in the "Input data" and "Output data" widgets in the WD

Scenario:

1. Open the Workflow Designer.
2. Add the "Classify Sequences with MetaPhlAn2" element to the scene.
3. Open the "Input data" widget in the Property Editor.
   Current result: there is gray space in the widget (see the attached screenshot). The gray space disappears, if the widget is resized.