It's majestically called diode logic, which means it's a free-for all except that signals from one source can't back up into another source. There is no handshaking because that would require microprocessor operation. IR signals are just a series of voltages that come out, only out, of a remote, get converted to a pulsing voltage that goes down a line instantaneously. There is no processing of any sort to be sure these things don't overlap.

It's surprising that a trigger code from outside could turn off a receiver in the middle of a macro, but that's only because I'm thinking from the standpoint of what commands I would tell it to do, not from what it would respond to. That is indeed possible.