wrong subnet mask - no free leases

[#1]

On one of our /25 subnets one of the members doesn't want to assign leases.
According to syslog the member thinks there are no free leases.

DHCPDISCOVER from xx:xx:xx:xx:xx:xx via bond0 TransID 0b847e9f: network 10.102.82.0/24: no free leases

If I put the DHCP range from FO association to the failing member, I do get a correct subnet mask in the syslog.

DHCPDISCOVER from xx:xx:xx:xx:xx:xx via 10.102.82.253 TransID 81555b1e: network 10.102.82.128/25: no free leases

So, I put the member showing the correct subnet mask as the single member for that subnet and now all clients are getting an IP.

Why is there a difference in the recognition of the subnet mask between those two members?