When editing a list using "Update Selected" or "Update All", if there is an active Business Rule intended to set a value on a read only field (for example copying the value from another field on the same table being listed), this will fail and the value will not be set.
Editing the record in any other way, like form view, list view, or client scripts, will work and the value on the target read-only field will be set.
Steps to Reproduce
Notice that only "Base field" and "Read Write" fields get updated. The same happens when using "Update All" rather than "Update Selected". The read only field is not being populated when using "Update Selected" or "Update All", even though the Business Rule is executed and the debug log shows the value being set.
Related Problem: PRB837902