[Tim Wood]

I haven't hit this case -- I suppose NSData could be doing a coordinated read in this case, which might cause file presenters (maybe including the document) to be asked to yield to readers (writing their changes).

I don't see anything in the documentation about NSData doing coordinated reads in this case, though. Presumably the TextEditor sample could be changed to replicate the problem -- it would be interesting to see if hear if you hit the problem in this case.