Problems switching to EXTERNAL_SLOT_2 on WP8548/WP7502


We have the same problem with WP8548 (on mangOH Green, primary CF3) and WP7502 (on our custom board). Using ‘cm sim select’ command we can’t switch to EXTERNAL_SLOT_2. E.g.

login as: root
Linux swi-mdm9x15 3.14.29ltsi-5d7a6bf7c6_ed88cc68b5 #2 PREEMPT Sat Feb 6 02:37:18 PST 2016 armv7l GNU/Linux
root@swi-mdm9x15:~# cm radio
Power: OFF
Current Network Operator:
Status: Not registered and not currently searching for new operator (LE_MRC_REG_NONE)
Signal: No signal strength (0)

root@swi-mdm9x15:~# cm sim info
ICCID: 89701202115300878591
Home Network Operator: Tele2 RU
IMSI: 250202106237359
Phone Number:
root@swi-mdm9x15:~# cm sim select EXTERNAL_SLOT_2
root@swi-mdm9x15:~# cm sim info
Home Network Operator: MegaFon RUS
Phone Number:
root@swi-mdm9x15:~# cm sim
SIM card is absent (LE_SIM_ABSENT).


But when we reboot the board with the EXTERNAL_SLOT_2 selected, ‘cm sim info’ gives us meaningfull information (after reboot completed), ‘cm sim’ reports READY for the second slot and we can establish a connection using ‘cm data connect’ command. When we switch from SLOT_2 to SLOT_1 and back then SIM 2 is reported as ABSENT again (until next reboot). SLOT_1 is always reported as READY.
Could anyone help? Is there a tricky command sequence?
root@swi-mdm9x15:~# cm info firmware
SWI9X15Y_07.12.14.00 r34472 CARMD-EV-FRMWR1 2017/11/29 18:24:42