Vlookup 'looks up' duplicate values in error

I have used vlookup find values from the table below

1 20 to return cloumn 2 figures for 1
2 30 2
3 40 4
4 50 7

Where 7 is not in the list, I get the duplicate of the value in column 2 above ie 1 20
2 30
4 50
7 50
using vlookup(a2,range,2,true). I realise this may be quite simple but an explanation would be of great help

Cheers Steven