Burnley are expected to bring around 1500-2000 aren't they? That would mean that they'd need about 3-4 blocks, so S1B - S1D (and possibly half of S1E) are the Burnley sections, with the remainder of S1E as a buffer. So sounds sensible that no more South stand tickets would be made available.
I don't think there will be any Burnley fans in S1E. Could be wrong though.