Quanah,
So Stanford also uses SASL/GSSAPI, and is hitting a similar issue, except on read instead of modify. When I take SASL/GSSAPI out of the picture, the search works fine. Are you able to test doing a simple bind with the modify to the server and seeing if that works?
I can confirm the operation works just fine with simple bind. With all the testing you've done, it doesn't give me a warm fuzzy feeling that this was some simple bug introduced anytime recently.
Mark