Array Formula only works if entered in more than one cell

I've seen this happen once before (on a shortest formula challenge)

I am working on a solution for http://www.excelforum.com/excel-form...h-vlookup.html

Every solution I have come up with does the same thing, it will work only if array-entered into multiple cells at the same time.

Formulas this holds true with are:
=SUM(INDEX(F3:F23,MATCH(B3:B17,E3:E23,0))*C3:C17)
=IF(NOT(B3:B17="-"),SUM(INDEX(F3:F23,MATCH(B3:B17,E3:E23,0))*C3:C17),"")
=SUM(VLOOKUP(B3:B17,E3:G23,2,0)*C3:C17)



Why is this? The formulas work perfectly, if entered into more than one cell (ANY number of cells). But do not return the right result when only entered into one.

I think VLOOKUP's don't work well in array format but INDEX/MATCH should as far as I know?