I don't have an easy way to capture the back-trace and pull it from the machine right now, so I've attached a screen-cap and hand-transcribed salient bits:
The system was a fresh install of CURRENT downloaded last night, put on a Dell Inspiron i1420 with pretty default configuration (one whole disk GPT partition with a boot, / and swap configuration) mostly just to test some jail stuff. Only new packages installed were zip/unzip/bunzip/bunzip2 so I could uncompress the Handbook (html-split). It was triggered in /usr/share/doc/handbook/html (the last two subdirectories being subdirectories I'd created to house the handbook). The error was triggered by executing "tar xf book.html-split.tar"
Created attachment 166558 [details]
Screen capture of error, traceback and output of "uname -a"
For some reason the original didn't attach when creating the case, so I shrank it to 30% to see if it was a size issue and am retrying the attachment.
This is a known 'false positive' in Witness. We do not currently have a good way to supress this message even when it is a known false positive.