Yes, the devices have the following power-down requirements:
If powering down in standby sleep mode, to properly detect and recover from a V_DD brown out condition any of the following actions must be taken
• Ensure that VDD falls below 100mV before powering back up.
• Bring the device out of sleep before powering down.
• Set the No Buzz bit in the OSC_CR0 register to keep the voltage monitoring circuit powered during sleep.
• Increase the buzz rate to ensure that the falling edge of V_DD will be captured. The rate is configured through the PSSDC bits in the SLP_CFG register.
For the referenced registers refer to the Technical Reference Manual. In deep sleep mode, additional low-power voltage monitoring circuitry allows V_DD brown out conditions to be detected. For edge rates slower than 1V/ms, these requirements are not necessary in deep sleep mode.