Hi
This is because .32 is not part of your 10.20.4.0/27 subnet. Think of it like this.
/27 = 255.255.255.224
256 - 224 = 32 so your subnets go up in 32's eg.
Ist subnet = 10.20.4.0 255.255.255.224
2nd subnet = 10.20.4.32 255.255.255.224
3rd subnet = 10.20.4.64 255.255.255.224
etc...
So .32 is the network address of the next subnet.
Just for completeness you shouldn't really use .31 as an IP address of a host either as this is the broadcast address for the 10.20.4.0/27 subnet.
HTH
Jon