base/releng/10.1/UPDATING r284193 have a typo at a patch number. It's written "p29", but it have to write "p11". I think "p29" is the number of 8.4-RELEASE-p29.
Created attachment 157606 [details] A patch to rewrite "p29"->"p11" I forget to paste a patch. Sorry.
Fixed in base r284230.