Calling all VBA geeks

Ok, I need some VBA expertise here. I'm writing a bunch of macros inside Microsoft Excel, and I came across an unfortunate catch. Let's say you start a subroutine like this:

Sub XYZ()
     Dim abc As Integer
     abc = WorksheetFunction.Lookup(yada, yada, yada)

Now, if you make the next line

     Dim lookup As Variant

...then you will "poison" your namespace such that the previous line will immediately change to

     abc = WorksheetFunction.lookup(yada, yada, yada)

Deleting the "Dim lookup..." line doesn't fix the problem -- it appears to be a permanent change. The only fix I can find is to create an entirely new workbook and manually copy over all my modules.

Anybody know how to, in essence, repair my namespace?