If you install Studio 6.2.0 (recommended - it fixes some niggling problems in the prior releases [did not remember parameter values or data source]) you may find that the backspace key acts a 'delete-on-right' rather than 'delete-on-left'.

You need to remap the key.  See http://community.jaspersoft.com/jaspersoft-studio/issues/6451 comment #5

Regards, Tim G