This has happened to me when I have needed to manipulate the rs for 
reporting purposes, where any changes are not posted to the database.
Usually on a field that I have created in a sp and set to a specific value 
i.e '0 as qtyNeeded', the only way I have found to get round this is to 
use a field from a table referenced in the sp of the same data type as 
that you require i.e 'Qty as qtyNeeded'; as long as I am aware that the 
retrieved values in this field need manipulating before they make any 
sense I have no problems!

Hope this helps.

Tim Perkins