Trying to change chapters by selecting the book from the top center menu in 'reading' mode causes Mantis to immediately quit. But, once restarted, it will open to the book/chapter selected. Happens every single time. Latest iPad version on a 3G 64GB iPad.

This should not be happening. First thing to try would be to reboot the iPad (hold down the top button and the home button and keep holding both buttons until the Apple logo appears, then release both buttons.)

If this does not solve it, then we suggest you reload Mantis on the iPad. First back up any bookmarks and notes using the "Backup" button the Bookmarks screen, then delete Mantis from the iPad and download it again from the App Store.