From the Installation summary:

1. click on Booting
2. uncheck "install generic code to MBR" and "set active flag on partition"
3. click on OK/apply/whatever the text is
4. the printed text on the summary matches what you set
5. click back on booting and both boxes will be rechecked

Also, the active flag is set on the partition regardless of any setting (there
is no text to confirm it's setting).

I'm not sure if it listens to the generic MBR code setting -- the check box
says it isn't, but the text says it is.