2) MAC addresses can, in most circumstances, be programmatically assigned, i.e. the OS can override and replace the hardware MAC address with an arbitrary software MAC address.
Negative Sir. Only in very high end hardware can MAC addresses be programmatically re-assigned. In the above ARP table 50:e5:49 relates to the manufacturer of the NIC chip used on Gigabyte Motherboards. In the examples shown in the ARP table Realtek PCIe GBE Family Controllers.
In my recent experience with a few top-end HP servers and possibly even the Dell boxes the MAC addresses were fixed by the chip manufacturer. I have heard that some Cisco routers enable their MAC addresses to be changed, but not on your average Joe Public kit. Some systems allow a sysadmin to mask a MAC address, but it doesn't change the underlying address, only what appears to the system temporarily.
I agree MAC addresses have nothing to do with the OP's original issue.