9.2.4 BOR and Bulk Erase
BOR is forced ON during PFM Bulk Erase operations to make sure that the system code protection cannot be compromised by reducing VDD.
During Bulk Erase, the BOR is enabled at 1.9V, even if it is configured to some other value. If VDD falls, the erase cycle will be aborted, but the device will not be reset.