issue with bootloader unlock after root

Hi,
I had and have a strange behaviour of the locking status:
What I did first after buying my used Z5C (5823) 3 weeks ago:
1) Downgrade to LP E5823_StoreFront_1299-6910_32.0.A.6.200_R2B
2) Created TA.img with iovyroot (as found out later, it didn't contain DRM keys and was unlocked....so the TA.img is useless)
3) Upgraded to E5823_32.2.A.0.224_Custom
4) patched and flashed the .224 Kernel with SuperSU, TWRP and no BusyBox, DRM
5) flashed back the - useless - TA.ftf

After this, whenever I open the service info/configuration ist shows 'bootloader unlockable: yes' or 'bootloader unlocked: yes' or 'bootloader unlockable: no'. I didn't find out, which situation leeds to which result.

So today I
1) flashed the E5823_32.2.A.0.253_R2C_Customized DE_1298-1220 with full wipe
2) flashed the TA.ftf, to check out if has really an unlocked bootloader (-> yes)
3) patched and flashed the .253 Kernel with SuperSU, TWRP and no BusyBox, RIC off and DRM -> SuperSU OK, DRM keys OK

Right after configuring the phone for the first start, bootloader was unlocked.
After 30 min bootloader was unlockable again.
????????

Is it quite normal, I guess no.
Any solutions??

Thanks from germany!!!