MacOSX 10.6.8 Startup Disk System Preference bug (and solution)

Just found out about a weird MacOSX 10.6.8 Startup Disk System Preference bug. Whenever you try to install MacOSX 10.11 on another partition or volume from MacOSX 10.6.8, after the install the Mac boots from the new MacOSX without problems. But as soon, as you try to boot again from your old system 10.6.8 by selecting it in the Startup Disk System Preference, the problem begins. It boots from MacOSX 10.6.8, but in the Startup Disk System Preference on MacOSX 10.6.8 the Mac does not see the newly created MacOSX 10.11 volume anymore. This is definitively a bug. You can circumvent it by restarting and pressing the option key, so you can choose, from which volume you want to boot.