I have a Moto Z3 Play with stock ROM and rooted it by Magisk. Phone is seamless updates and treble ready. Everything works fine. Yesterday system updater was trying to update to the newest version but it fails. I know, I changed boot partition so it can fail. I downloaded a full ROM zip file from Lenovo servers (PPWS29.131-27-1-15), unpack it and trying to flash the newest version by myself using fastboot.
The current slot was B, it contained PPWS29.131-27-1-11 version. So I changed to A and flashed all partitions from PPWS29.131-27-1-15 ZIP file on slot A.
Commands that I used to flash PPWS29.131-27-1-15:
fastboot getvar max-sparse-size fastboot oem fb_mode_set fastboot set_active a fastboot flash partition gpt.bin fastboot flash bootloader bootloader.img fastboot flash modem NON-HLOS.bin fastboot flash fsg fsg.mbn fastboot erase modemst1 fastboot erase modemst2 fastboot flash bluetooth BTFM.bin fastboot flash dsp dspso.bin fastboot flash logo logo.bin fastboot flash boot boot.img fastboot flash system system.img_sparsechunk.0 fastboot flash system system.img_sparsechunk.1 fastboot flash system system.img_sparsechunk.2 fastboot flash system system.img_sparsechunk.3 fastboot flash system system.img_sparsechunk.4 fastboot flash system system.img_sparsechunk.5 fastboot flash vendor vendor.img_sparsechunk.0 fastboot flash vendor vendor.img_sparsechunk.1 fastboot flash oem oem.img fastboot erase carrier fastboot erase ddr fastboot oem fb_mode_clear
Then I tried to boot from A slot but it fails. The phone got bootloop and lands in stock recovery. I assumed that something goes wrong so I rebooted to bootloader and changed slot to B to boot PPWS29.131-27-1-11 version which was working fine. And then comes mindf*ck - after system start from slot B, I noticed that system version is now PPWS29.131-27-1-15. But how? I flashed partitions on A slot, not B. Even fastboot logs showed that I was flashing A slot.
When I changed slot to A with fastboot command is it really flash A partitions? Or just change which partition should boot in the next reboot?