Yes, this is a limitation of Filemaker Go. This issue has been reported before, but I don't think FM is calling it a bug, even though I would consider it a bug because there is a option to print without a dialog and it will not print without a dialog box.
Foundryis and S Chamblee:
Thank you for your posts.
At this time, Printing without dialog in FileMaker Go 12 will still bring up the print dialog box. FileMaker Go hands over the print request to iOS, and we currently have no further control.