Why I mustRefresh instead of partial refresh when trying to unselect feature?

Question

Hi friends,I am new to the arc object and the engine.
    Using 'IMapControlDefault.ActiveView.PartialRefresh(esriViewDrawPhase.esriViewGeoSelection, null, null);' or 'IMapControlDefault.Refresh(esriViewDrawPhase.esriViewGeoSelection, null, null);' does not work at all.
    using 'IMapControlDefault.Refresh();' or 'IMapControlDefault.ActiveView.Refresh();' instead will work.
    I have searched informations on the esri help document,but it seems none suit or can explain why.

kju · Answer

Any time you call PartialRefresh you must call it twice.  You must call it once before you do whatever will need refreshing and you must call it once after you do it.

Thanks for your response,It seems not that much hard to understand the 'PartialRefresh' before and after operation.But sometimes I  gonna think that why it work when using Refresh instead of PartialRefresh.

NeilClemmons_GISinc · Answer

Any time you call PartialRefresh you must call it twice.  You must call it once before you do whatever will need refreshing and you must call it once after you do it.

kju · Answer

Hi friends,I am new to the arc object and the engine.
    Using 'IMapControlDefault.ActiveView.PartialRefresh(esriViewDrawPhase.esriViewGeoSelection, null, null);' or 'IMapControlDefault.Refresh(esriViewDrawPhase.esriViewGeoSelection, null, null);' does not work at all.
    using 'IMapControlDefault.Refresh();' or 'IMapControlDefault.ActiveView.Refresh();' instead will work.
    I have searched informations on the esri help document,but it seems none suit or can explain why.

Can somebody help? 
Refresh is not the only way,it also work if PartialRefresh the Selection before and after the ClearSelection.I hope someone can help me explain why.