Customizing a DMG build is an iterative process. Therefore it is necessary to open a generated DMG several times in order to see whether everyting is OK. Now the problem is that any further build will fail silently without any error message if the user just closes the previous window but forgets to eject the DMG itself too. A new DMG will then be created but it will be broken and the reason for this may not be obvious for the user. In order to fix this issue one should at least issue an error message and abort the faulty DMG creation if a disk with this name is already/still mounted. If technically feasible it would even be better to silently eject any disk which has the same name as the to be created DMG before a new creation starts. This would avoid this pitfall and would result in a better user experience.