[qualiteam]

Unfortunately, it is impossible to test design updates on every possible configuration. That's why the generic fixes that we release will work for many users, but someone will have to apply extra CSS tweaks to get the changes compatible with their setups.

The XC5 dev team have plans on adding the fourth number to XC5 versions. Minor tweaks that will likely not affect most of the users will go into that number. Also, there are three waves of releasing a new version ("live" stores get the update on the third wave only).

Although the above should minimize the risk of installing an update that breaks some custom design themes and/or modules, the good practice is testing the update on a dev copy of your site so that you could tweak your theme and custom modules before upgrading your "live" store.