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#21
EFI bioses will change a boot order without input from the user. Depending on whether you have media in the DVD or not, different options will be offered. Same type of thing with a Flash drive. But as long as the media is present, it should maintain the order, and this would be for situations like installs.
My suggestion is to always use the Boot device menu to make sure what you are booting to.
Edit: If you want, there is a setting in the bios on the boot page that will set which type of system you want to boot. If you go with MBR, you can set it to boot Legacy only and you won't have to worry about any UEFI boots.