MSP432 SRAM memory retention in LPM3

Hi

SRAM doesn't seem to keep its state in LPM3. 

Here's my code:

#include "driverlib.h"
#include <stdio.h>
#include <string.h>


uint8_t buffer[20000];


void main(void)
{
    // init code
    [...]

    SYSCTL_SRAM_BANKEN |= SYSCTL_SRAM_BANKEN_BNK7_EN;       // enable ALL the memory banks
    SYSCTL_SRAM_BANKRET |= (SYSCTL_SRAM_BANKRET_BNK1_RET |
                            SYSCTL_SRAM_BANKRET_BNK2_RET | 
                            SYSCTL_SRAM_BANKRET_BNK3_RET |
                            SYSCTL_SRAM_BANKRET_BNK4_RET |
                            SYSCTL_SRAM_BANKRET_BNK5_RET |
                            SYSCTL_SRAM_BANKRET_BNK6_RET |
                            SYSCTL_SRAM_BANKRET_BNK7_RET);    // enable retention for ALL memory banks
    __delay_cycles(1000000);    // wait some time

    memset(buffer, 0x7d, 20000);

    Interrupt_enableMaster();
    SCB_SCR |= SCB_SCR_SLEEPONEXIT;
    // enter LPM4
    SCB_SCR |= (SCB_SCR_SLEEPDEEP);
    __sleep();
    __no_operation();

    // wake-up triggered
    char tmp[32];
    sprintf(tmp, "@0x%x: 0x%x ", (uint32_t)buffer, buffer[0]);
    print_string(tmp);
    sprintf(tmp, "@0x20001fff: 0x%x ", *(uint8_t*)(0x20001fff));
    print_string(tmp);
    sprintf(tmp, "@0x20002000: 0x%x ", *(uint8_t*)(0x20002000));
    print_string(tmp);

    while (1);
}

When I flash the program code and let it run, the output is  0x7d for all 3 memory addresses. However, after resetting the device, the output is different:  I get 'random' values for the last print line, which tells me that bank 1 of SRAM (starts at 0x20002000) does NOT retain its state. 

Regards,

keepcoding