Hi,
As you mentioned the '+' symbol will appear as heading for non-key fields in the table maintenance generator ,
I don't know the exact reason why it appear like that.
But you can get the heading by the following way,
In Change mode of table maintenance screen,
Utilities->Table Maintenance Generator.
In the Next screen use menu path,
Environment->Modification->Maintenance Screens
Here Click on LAYOUT Button.
It will give you a Module Pool screen.
There you set the TEXT property for the the required fields.
In this way you can get the headings.
Regards,
Anil.
