Last week we found a Reporting Services graph which all of the sudden was showing double entries. Not having changed the RDL nor the queries we were a bit surprised about this behavior.
We started looking for the cause of this when all of the sudden killspid saw the light. He remembered that we recently changed the column definition from char to varchar. Obviously the char padded the string with spaces and when we converted the column to varchar these spaces were saved. The string "XXX " is most certainly different from "XXX".
A simple UPDATE tblTable SET myField = RTRIM(myField) solved our problem.
It doesn't always have to be rocket science now does it? :-)