By default the timezone of Timestamp fields in reports are adjusted based on timezone selected by user. This can be disabled in non-Ad Hoc reports by adding either
to ../WEB-INF/classes/jasperreports.properties file.
These properties are documented in [JR Configuration Reference|http://jasperreports.sourceforge.net/config.reference.html]
For Ad Hoc reports however you need to configure the timezone adjustment in applicationContext-formatting.xml (in addition to setting the properties above):
To disable the timezone adjustment you have to set all four entries to "false".
This property is not documented anywhere, and it will be helpful to have it, for example, in JRS Admin Guide.
*Additional notes*: there is a defect with timezone adjustment when exporting Ad Hoc Views and Reports to one of the available output formats. This is fixed and should no longer be an issue starting with the next version.