Description of Problem:
When pressing back on the bootloader configuration screen and
then next again, all the settings are forgotten and reset to
the default value.
In addition, the boot label for the Linux partition is set to null
and "Default boot image" is not set (therefore you can't even press
"next" until setting the values again).

How Reproducible:
100%

Steps to Reproduce:
1. run GUI installer
2. go to "bootloader configuration screen"
3. select something that differs from the default settings
4. press back
5. press next