PivotTable referring to old column names

Hi,

I am working on a PivotTable, and I had it mostly working the way I wanted.

I made a change to the source data.  Among other things, my data had a "First Arg" column and a "Description" column.  But, due to  the nature of the data, each row would only have one or the other.  So, I changed my source data table, and merged these two columns into one column "First Arg/Description".  So far, so good.

But, when I create a new PivotTable, in the Field Names list, it still shows two distinct names, "First Arg" and "Description".  I'd expect to see one Field Name, "First Arg/Decription", which is what I now have in the source table.  Not sure what's gping on here.

Help?