Update: This has nothing to do with publishes. It just seems to have randomly when things are changed on the page (i.e. 2 drafts are created). The newest draft is always a copy of the published version and therefore in affect the changed made have been lost as the 2nd draft cannot be published.

Managed to see what web requests the browser was making when one of these duplicates is created. Some sensitive information has been removed:

{}&&{"isCommonDraft":false,"allowToDelete":true,"contentLink":"13663_191377","language":"en","name":"uk investor","savedBy":"xxx","statusChangedBy":"xxx","savedDate":"2014-11-04T11:00:16.6Z","uri":"epi.cms.contentdata:///13663_191377","status":2,"statusName":"Draft","typeIdentifier":"xxx.webtech.templates.models.blocks.acctabitemblock"}

 {}&&{"successful":true,"savedContentLink":"13663_191376","publishedContentLink":null,"properties":[{"name":"content","value":"xxx","successful":true,"validationErrors":null,"committed":false}],"validationErrors":[]}

{}&&{"isCommonDraft":true,"allowToDelete":true,"contentLink":"13663_191376","language":"en","name":"uk investor","savedBy":"xxx","statusChangedBy":"xxx","savedDate":"2014-11-04T11:00:14.46Z","uri":"epi.cms.contentdata:///13663_191376","status":2,"statusName":"Draft","typeIdentifier":"xxx.webtech.templates.models.blocks.acctabitemblock"}