Version of MW: 1.20-xxx and probably as far back as usercontribs is available in the API

Because a bot or possibly a script-assisted user may edit more than once a second, use of the ucstart parameter returned in <query-continue> tags to retrieve the next bach of changes may retrieve some changes already seen in the previous batch. For example, see below:

zh.wikipedia.org/w/api.php?action=query&list=usercontribs&ucuser=Liangent-bot&ucstart=2012-04-07T07:44:45Z

This returns ucstart of 2012-04-07T07:44:44Z but some of those changes are already in the current result set. Retrieving the new url gets some dups:

http://zh.wikipedia.org/w/api.php?action=query&list=usercontribs&ucuser=Liangent-bot&ucstart=2012-04-07T07:44:44Z

Suggested fix: add a revision id or other tag from what would be the first row of the new result set, to the end of the parameter in these cases:
ucstart="2012-04-07T07:44:43Z|20655891"

The revid is risky if the revision is hidden or deleted by the time the new result set is requested; perhaps there's some better unique tag that can be tacked on to the parameter instead.

Version: unspecified
Severity: normal