If I edit an entity (e.g. see https://www.wikidata.org/w/index.php?title=Q4115189&action=history around 20:13, 10 June 2015) and then restore previous data, in the dump I have this:
wdata:Q4115189 schema:version "221944409"^^xsd:integer ; schema:dateModified "2015-06-10T20:13:41Z"^^xsd:dateTime ;
but in the database I have:
221944373 2015-06-10T20:12:48Z
Looks like update is somehow messed up when restore/undo happens.