There were some issues with that were solved in version 10.4.6.0, but now I have similar issues with EditorType edComboEdit & edComboList on Post operations. (now using latest version - 10.5.3.0)
If inplace editor is active and you press the dbnavigator Post , you get unexpected behaviour.
It doesn't work well unless you press ENTER in the cell before pressing Post in the navigator.
I also had distinct results with design-time created grid column vs runtime created column.
For a design-time created column, it posted the change on the first click, but navigator buttons states were not updated. Looked like having pending updates.
Video: IDE created column edComboList issue
For a runtime created column, it doesn't post the changes neither update navigator buttons state, and brings back the original value to the cell.
Video: Dynamically created column edComboList issue
Anyway, there's still something missing when an inplace editor is still active and you try to use navigator actions before forcing it to loose focus.
(The grid has PageMode, epRow, nonsequenced, RefreshOnInsert, RefreshOnDelete, AllowInsert/DeleteRows, AdvanceInsert=False, AdvanceOnEnter, adLeftRightInRow).