In our project we have several read-only checkboxes in the review section. There are standart True/False tooltips over them that should be deleted. These checkboxes don't have any custom presentation parameters.
A quick workaround could be to make the edit options to "Auto" under the Presentation tab, then go to General tab and you will see the tooltip text box appears. Remove the text from there. Now come back to Presentation tab and make it again read only.
What does the tooltip say? Might it be one that is presented out of the box by Pega as an accessibility feature? (allowing for sight-impaired users who are using your application to better access the screen using a screen reader)