DHCP static leases are NOT working.

Hi there!
I have problem to set up some static DHCP leases.
I set up router with QuickSet. , allowed DHCP 192.168.7.1 on LAN (bridge) set up dhcp range 192.168.7.100-192.168.7.255
Everithing works fine except of DHCP static leases.
When new device got his IP from DHCP, i selected “make Static”, then i edited record and set up address above xxx.200 outside free pool. Then i selected reboot router (i expect that it saves actual leases to flash).
But when device requested IP again, they use different IP (from free pool).
Only device NOT jumping to new IP are somer DEBIAN PC ane one from androids (Lenovo).
Second android (LG) and 4xWIN) are travelling in free pool instead of using reserved IP in DHCP static leases.
I tried to make reservations inside of free pool without any progress.
I spent A LOT of time to trick it, but no sucess. I tried to play with some dhcp setting (lease time, storing to disk , authoritative etc)
I am really sick and angry…grrrrr!!
I am not router geek, but i understand what i am doing, i configured previous router (older Router OS) without any problem. I discussed it with a geek without progress.
I use:
RouterBOARD 941-2nD
RouterOS 6.41
I tried to use upgrade to 6.42rc9 or downgrade to 6.39.3 without any effect.

By the way: there is something weir around setting DHCP range
1)You will be able to do it only in quic setup menu, not in dhcp menu
2)it is nearly impossible to change range after being set to some values
e.g. i set it for xxx.100-xxx.190,
then i tried to set it to xxx.100-xxx.180 but it allways returned back to xxx.100-xxx.190.
etc.
sometime it converted to notation xxx.100/32 or so…
Can you help me, please?