The Issue
After you type a value into a field in Pitch 'n Time Pro or LE you can press Enter or Return to send that value through to the plug-in.

When pressing Enter in a Pitch 'n Time text field the editor (or text field) remains active, therefore pressing Delete will delete the value in the text editor instead of your selected region in the Edit Window.

Workaround
Click somewhere outside of the Edit box, it will deselect the input field and you will then be able to delete a region of audio on the timeline in Edit Window using the Delete key.