I don't recall seeing any official explanation from the club. I'm pretty sure we started selling a bigger allocation than we ended up with though (?). The only other explanation I can think of is that the club mistakenly started selling a block that, it turns out, wasn't allocated to us and upon realising (coincidentally at the same time the fixture date was changed) they swapped things over. Actually, that sounds far less plausible than the baffling 'sent back a whole block of tickets because the date changed' scenario. Surprised no-one's quizzed them about this in twitter land yet (or perhaps they have and received no answer?)