Deleting fields from shapefile scrambles field values

I have a shapefile with approximately 70 data fields. When I delete a field in the table view (right click on field heading > delete field) the actual data in the remaining fields gets mixed up, ie some of the data moves over and appends to the field to the right. Has anyone else experienced this? It is reproducible. Thanks in advance.

Using ArcGIS 10.1 with SP1