I have to clarify something.
your test setup itself is based on an invalid network configuration.
I know it is invalid, it is for test purpose.
and then connecting the windows machine to one of the ports ether1..ether5 you are creating a network setup that can never work correctly.
Yes, I know !
I am solving ARP replies messing MAC tables.
Let's assume you connected the windows machine to ether2 on the router.
Now there also are addresses 192.168.103.12, 192.168.104.12 and 192.168.105.12 connected to ether2 but the router can not handle this correctly because it expects these addresses to be directly connected to other interfaces (ether3..ether5).
You are right.
.. and should not send a single packet with these IP addresses on ether2 (ARP too).
Clients that are physically connected to ether2 can not have an address that falls into a network that is associated with an interface other than ether2 on the router (unless that other interface is bridged to ether2, and even then the router's IP address would be installed on the bridge interface instead).
In my case these are not clients, but aliens and I do not want send any packet (ARP too) to them on ether2.
All of this is not MikroTik specific but just the rules of correct IP networking.
Yes, but we are not living in a perfect world and not whole network is in our hands.
And problem still remains.
I asked many people and everyone said it should not happen from Mikrotik.
grzesjan wrote it is possible to solve it on Linux.
So it must be possible on RouterOS too.
When you set ARP ether2 to "reply-only", it works correctly.
In this case ARP for IP on ether2 works and other IP ARPs are ignored.
That is how it should work.
Problem is I have to make complete static ARP table for ether2 and it is not very good solution.