The question I have is about the general functionality of the back button in wizards. I was thinking about the possible behaviors of this button and I couldn't find any clue which one is the right choice between these two options.
1- It should show the previous page and the changes made in the current form shouldn't be saved.
2- It should show the previous page and the changes made in the current form should be saved.
I would like to know which option you think is the correct behavior for the back button and why.
The pretty sensible Windows guideline from Microsoft is;
Preserve user selections through navigation.
For example, if the user makes changes, clicks Back and then Next, those changes should be preserved. Users don't expect to have to re-enter changes unless they explicitly chose to clear them.
See UX Wizards guide.