Rick's example is indeed an example of a topology to which I alluded. Also note, although Rick mentions redundancy, in reference to my posting, redundancy isn't required.

Again, Rick's is a fine example, and his example doesn't mention redundancy. The issue is whether the switch carries (two way) transit traffic for the hosts involved.

BTW, an interesting case of where even transit switches can "drop" MACs is in unicast flooding. See case number 1 in: https://www.cisco.com/c/en/us/support/docs/switches/catalyst-6000-series-switches/23563-143.html?dtid=osscdc000283