When exporting a book to PDF from Indesign CC2019 on Mac OSX Mojave, the export pdf dialogue box ("Generating PDF") displays (showing progress / page count) but it can't be hidden (or covered over) by switching to another app or browser window like it used to. Eg if it was z layers in CSS, it is always sitting on top and getting in the way of multi-tasking whilst exporting the book file.