A TIB_ComboBox is uses as an editor control in a TIB_Grid.

IIB_GridWinControl.GetText is descripted in help as "Return text that
will be displayed by the control."

The implementation function TIB_CustomComboBox.IBG_GetText is
descripted in comment as "GetText is supposed to return the
untranslated value of the field".

So what description is the right one?

Now, when inserting a new row in a grid and step from a CombobBox
Field to the next, the Combobox Field shows only the value of the
Field, not the "Value displayed by the control".

So 2 possibilities here:
1) a bug in the implementation of IIB_GridWinControl.GetText
2) a bug in TIB_Grid

I think 1.

Andreas