For the moment mass update works inconsistent for different lists and is not user friendly at all.
For example, in Items mass update Replace Applications: If checkbox is checked and multi-select left empty, submitting such form will remove all applications from all selected items. (All apps will be replaced to empty value). There will be no any success message or alert about you are going to delete applications.
It might be useful to have two fields for replacing - which item replace to what.
Also checkbox "Select all", like "Replace all" to... , "Remove All", etc. might be useful.
In case when we are about to delete some big amount of items Alert message might be shown.
When adding applications we can create new app in the same filed, but when replacing it is not possible.
These features need to be standardized and fetched to consistency, also made more user friendly and predictable.