Hi Graeme,
I believe this user is trying to cleanup his "artwork" from the last days. However he done it the most unfortunate way - only deleting the objects, that he added. If he used the proper way of reverting the changesets (or at least asked more experienced users at our [osm_sk] mailing list to do that), then it would also recover the ways, that he has destroyed in his changesets.

So I'm now checking his changesets and doing partial reverts to undelete those ways.

It is nice to know, that DWG is watching closely such suspiscious changesets. Keep up the good work ;)

Best regards,
Tibor from Freemap Slovakia, OSM local chapter