MSP430FR5994: ADC12_B Wake-up from LPM1 with MODOSC

I am struggling to wake-up from LPM1 with ADC12_B running on MODOSC.  The code sample is in Mecrisp Forth but self explanitory.

Set IRQ to wake-up:

['] wakeup irq-adc ! \ # irq

Set CPU to use MODOSC (to preserve power)

$A5 1 $160 + c! \ KEY CSCTL0_H \ unlock CS
$24 4 $160 + c! \ SELS2 SELM4 CSCTL2_L \ SMCLK-LFMODCLK MCLK-MODCLK
$FF 1 $160 + c! \ LOCK CSCTL0_H

Set up and start ADC12_B:

  $00 $00 $01B0 + !     \ REFVSEL_1.2V REFCTL
  $02C2 $02 $0800 + !     \ ADC12SHP ADC12DIV6 ADC12SSEL0 ADC12CONSEQ1
                          \ ADC12CTL1 
  $0021 $04 $0800 + !     \ ADC12RES2 ADC12PWRMD ADC12CTL2
  $00C7 $06 $0800 + !     \ ADC12TCMAP ADC12BATMAP ADC12STARTADD07
                          \ ADC12CTL3 < 1 MHz
  $011E $2E $0800 + !     \ ADC12VRSEL1          ADC12INCH1E ADC12MCTL7 
  $019F $30 $0800 + !     \ ADC12VRSEL1 ADC12EOS ADC12INCH1E ADC12MCTL8 
  $0390 $00 $0800 + !     \ ADC12SHT03 ADC12MSC ADC12ON ADC12CTL0
  \ clear flags
  $0000 $0C $0800 + !     \ ADC12IFG0 clear 
  $0000 $18 $0800 + !     \ ADC12IV reset
  $0100 $12 $0800 + !     \ ADC12IER0 enable
  eint
  $0C $0800 + @ hex.      \ ADC12IFG0 print 
  $0003 $00 $0800 + bis!  \ ADC12CTL0 start ADC
  \ begin pause $01 $0D $0800 + cbit@ until \ ADC12IFGR0_H done?
  lpm1                    \ enter lpm1 only adc running
  on                      \ led debug
  

I can confirm that it does not exit from lpm1.  If I use a normal delay loop and wait for the flag it works fine. (commented code)

Is there a known issue with MODCLK stopping in lpm1?