UltraGrid row filtering

We are using UltraGrid in a WinForms application. Since upgrading from 2016.2 to 2017.2 (version 17.2.20172.2006) we are facing the problem that the default entries (Blanks) and (NonBlanks) in the drop down are not working any more when using the FilterUIType FilterRow. Using Header Icons the rows are fitlered as expected.

The problem can be reproduced in the sample app "RowFiltering" provided by Infragistics.

Any idea what the problem might be?