In the UML guide there is a warning about the importance of the ARCH=um in "make menuconfig ARCH=um" and "make linux ARCH=um" > Warning: The ARCH=um fragment is extremely important! This warning does not reside right under the code listing, where the two commands are used, bit I think it's better there. Patch to fix it is attached to this report.
Created attachment 38495 [details, diff] Patch to change the position of the warning box
Fixed in CVS. Thanks for reporting!