subnet mask and multiple subnets via 1 router

[guest]

we have a router that services 192.168.10.0/24

we want to split the lan into 4 subnets:
192.168.10.0/26
192.168.10.64/26
192.168.10.128/26
192.168.10.192/26

so that no subnet can talk to each other but each subnet use the router which is on 192.168.10.1

the first subnet is no problem. when we enter the router address into the other subnets as the default gateway, windows complains (as the router isn't on the same subnet) but lets you go ahead and everything appears to work.

is there any issue with doing this?

[guest]

Ref your question: Maybe the ARP poroxies the router's address across the VLAN's or maybe your VLAN switch has some layer 3 functionality.

Regardless of whether it works or not, the configuration you describe is purposefully, incorrectly applied!. Each interconnected network segment should have a layer 3 device and a default gateway that's within it's own subnet.

Be cautious: anomalies and misconfigurations turn into security risks and/or network problems.