Proposed resolution:

[depr.strstreambuf.virtuals], paragraph 19, replace the setbuf effects clause which currently says "Performs an operation that is defined separately for each class derived from strstreambuf" with:

Effects: implementation defined, except that setbuf(0,0) has no effect.

D.7.1.3, paragraph 19, says that strstreambuf::setbuf "Performs an operation that is defined separately for each class derived from strstreambuf". This is obviously an incorrect cut-and-paste from basic_streambuf. There are no classes derived from strstreambuf.