Proposed resolution:

In [depr.ostrstream.cons] paragraph 2 and [depr.strstream.cons] paragraph 2, change the first condition to (mode&app)==0 and the second condition to (mode&app)!=0.

D.7.4.1 strstream constructors paragraph 2 says:

Effects: Constructs an object of class strstream, initializing the base class with iostream(& sb) and initializing sb with one of the two constructors:

- If mode&app==0, then s shall designate the first element of an array of n elements. The constructor is strstreambuf(s, n, s).

- If mode&app==0, then s shall designate the first element of an array of n elements that contains an NTBS whose first element is designated by s. The constructor is strstreambuf(s, n, s+std::strlen(s)).

Notice the second condition is the same as the first. I think the second condition should be "If mode&app==app", or "mode&app!=0", meaning that the append bit is set.