Hi Phil and welcome to the forum,
A quick tip is to 'Undo Type' after the 'Paste' this will remove all formatting on the text.
Another option is to set the fields Auto-Enter options to run a calculation to remove the formatting.
Go into the database field definitions and highlight the field in question.
Now under the 'Auto-enter' tab click on the check box for 'Calculated value' a Specify Calculation dialog will appear and here is where you enter the calc to reformat the text to upper. Input the following
TextFormatRemove ( FieldName )
Deselect the option 'Do not replace existing value of field (if any)' so the calc will run whenever the field is modified.
And click 'Ok'
Let me knopw if this works for you.