Looks like we can't reproduce the issue or there's a problem in the test case provided.
Ext GWT Premium Member
combo-box drop-down to be wide enough to show long values
Would like ComboBox to have the ability for the drop-down list to be as wide as the data in the list, even if the displayed column is not very wide. If users resizes column in grid, would like that not to have negative impact to a combo box in the grid.
Screenshot shows cropping of colors "mother of pearl" and "very, very dark red"...