Problem with DHCP and static entries

hi,

I'm running XG Firewall as home edition and now I have a problem with DHCP.

A client was connected to the firewall an got the IP .59.
Then I copied the MAC address an set up a static IP (.10) for it.
I restarted the client (Android Tablet) and ... it got the .59 again.
In the log I found "RENEW   Lease 192.168.178.59 renewed".

Next I changed the DHCP range to IP addresses from .70 to .100 and set the maximum lease time to 5min.
I turned off the client, waited 5min and than saw "EXPIRE - Lease 192.168.178.59 expired" in the log.
After that I turned on the client and ... yes I got an IP from the DHCP range again, this time .70.
The client doesn't get the IP address from the static DHCP entry.

I have the same problem with 4 other clients.
Only 1 client now got a the static IP address from the DHCP server.
I also checked several times if the MAC address is really correct - and yes, it was correct.

This is really driving my crazy!
I hope that someone in the community has an idea to help me.