LOOKUP Function: Bug or Finger Trouble

I have attached a spreadsheet that
        demonstrates my issue well.  Yes its complex.

Column A is a concatenation of columns B and
        C.  I use column A as a key for the cells in columns B and C.

Columns E and F represent how I want to use
        the list created by columns A..C.

Column E uses data validation pull down list
        to select the key from column A.  The LOOKUP function in column
        F is used to return thesubcategorymatching
        theselected key.  Only it doesn't
        always work as intended.

Have I found a bug or am I being a nob?

Many thanks

I have attached a spreadsheet

You haven't. I think you cannot add attachments on this list.