hi,
*** Code ***
F2 ->  PostAppEvent(xbeTab_TabActivate,,,oBox)


oBOX         := XbpPushButton():new(drawingArea,,...
oBOX:caption := "F2 S~ort"
oBOX:tabStop := .F.
oBOX:create()
oBOX:activate := {|| SetAppFocus(oCombo),;
                     PostAppEvent(xbeP_Keyboard,xbeK_ALT_DOWN,,oCombo)}

oCombo       := XbpCombobox():new(drawingArea,,...
oCombo:type := XBPCOMBO_DROPDOWN
oCombo:tabstop  := .T.
oCombo:create()

 Link data from entry field to LOCAL variable
oCombo:XbpSLE:dataLink := {| x | IIF(x == NIL,cIndex,cIndex := x)}
oCombo:XbpSLE:setData()
oCombo:XbpSLE:setInputFocus  := {| u1,u2,oSelf | oSelf:setMarked({ 
1,oSelf:buff...

 Code block for selection:
bAction := {| mp1,mp2,obj | cText := obj:XbpSLE:getData()   ,;
                            ...,;
                            setAppFocus(oOtherSLE)}

 Assign code block for selection with Up and Down keys
oCombo:ItemMarked := {|| NIL }

 Assign code block for selection by left mouse click in list box
oCombo:ItemSelected := bAction
*** Eof ***

i do press F2 -> PostAppEvent(xbeTab_TabActivate,,,oBox)
oBox use PostAppEvent(xbeP_Keyboard,xbeK_ALT_DOWN,,oCombo) to "open" 
Dropdown Part.

If Mouse is "over" Dropdown Part and i use Cursor up/down than 
oCombo:ItemSelected will be fired !!!
it does work if Mouse is NOT "over" Dropdown Part !!!

can someone confirm it ?

only workaround : use Mouse-API to "move" Mouse to other XbPart before 
"open" Dropdown Part.
greetings by OHR
Jimmy