Well, I hate to belabor the point or be this confrontational, but you are wrong, at least about me being wrong, but your refutation doesn't ever actually meet what I am talking about.
This is easily demonstrable.
1. Setup a unix/linux host with 2 IP's in the same subnet and one IP on a NetApp in the same subnet. Create an export rule for just one of the IP's on the unix host. Try to mount the export a few times. At random times it will fail.
2. Put a NetApp filer in a different subnet. Setup 2 IP's on the filer in that subnet. Setup firewall rules that allow for snmp requests to one of the interfaces. Run snmpwalks for a while. It might not fail right away, but at some point it will fail. The NetApp will answer from the IP/interface that is not allowed.
3. Just sniff the traffic from example one. Even add another IP on the NetApp side to make it even more interesting.
But basically, there is no difference between interfaces on the same subnet. If the OS chooses to initiate traffic from any one of them, it is behaving correctly, and to a point deterministically, that is, it is following routing rules, it is behaving correctly, but not predictably for a specific interface/IP. The OS just makes the choice.
This will basically work with any 2 interfaces in the same subnet. I guess I wouldn't be sitting here writing all of this if you had ever tried this. Even if I had 2 interfaces on the same subnet on this laptop, I couldn't, without some source route hack, determine which of them would contact this website. The OS would just choose an IP, because they have equal value in reaching the default gateway, because they are in the same subnet.
Basically, you are avoiding direct refuation. That connections have source and destination IP's is defined, but that is hardly the point here. Qualifying your arguments with "quite" and "pretty much" does seem to detract a bit from your contentions as well.
Anyway, like you said, we are wondering off topic here.