FileMaker Training Series 13 Advanced says:
"A popover object can be dismissed by clicking the popover button a second time or by clicking anywhere outside the popover object. The iOS Human Interface Guidelines recommend developers avoid providing a “dismiss popover” button. However, if the popover is being used for data entry, a button may be appropriate for accepting the input and dismissing the popover."
Do you consider that we should include a button in every pop-over to close it?
I think that some inexperienced users can feel lost without that button...