I recently found a strange error using VLOOKUP (actually, MATCH does the same):
In cell A6, type 0.1
In cell A7, type =A6+0.1 and copy down to A25
Copy A6:A25 to B6:B25
In cell C6, type =VLOOKUP(B6,A$6:A$25,1,FALSE) and copy down to C25
All looks fine, but now copy A6:A25, and paste...