Hi Leif,
I don't quite know what you mean 'lockup'. I made a test on my TWR-K24F120M. I download the example power_mode_switch by keil. In Project->option->debug->setting->Reset, I select 'reset pin'. Then I let the chip into VLLS2. Then I press the RESET button on KEIL. The SRS register will be 0x41.
Then in Project->option->debug->setting->Reset, I select 'Core and peripherals'. And do same operate as before, the SRS register read as 0x1.
So I didn't see any problem. Can you give more detail about your question?
Regards
Jing