Comment # 1 on bug 89148 from Stefan Dösinger

Note that the texture is never used as a source or destination in a regular
draw. It is specified with glTexImage2D, but the data pointer is NULL, and
glTexSubImage2D is never used. It is only filled with data through the FBO_blit
call that resolves the multisampled renderbuffer. As far as I can see no PBO is
used.