I can never remember what they are for, but at one point Epicor added to customization scripts the Extends alias lines at the top of customization. Some of them are now breaking customizations, because whatever they are for has been removed. I just remove all of them save the customization and they are good.
Secondary to that number field formatting something has changed with number formatting in places things are getting cut off in base screens.
So much for non-breaking but just be warned .28 was good as gold I would consider not doing .29 without running all customizations through validation.