SharePoint 2010 Document Library - Incorrect Version History Issues

Hi Friends,

When a user opens a document as a Reader (not checked out), views the document (in browser or in Office App) and then closes it-  the properties (version history, last modified by and date) of the document is updated- new version is written and the 'modified date' and 'modified by' is overwritten. Document version history is enabled to create a major and minor version.

At the moment there is no consistency/trend and I can not reproduce this issue. It appears to impact more than one document library.

Thank you in advanced.

Regards
Clint