During a red team assessment of an enterprise LAN environment, the tester discovers an access switch that connects multiple internal workstations. The switch has no port security measures in place. To silently intercept communication between different hosts without deploying ARP poisoning or modifying the routing table, the tester launches a MAC flooding attack using the macof utility from the dsniff suite. This command sends thousands of Ethernet frames per minute, each with random, spoofed source MAC addresses. Soon after the flooding begins, the tester puts their network interface into promiscuous mode and starts capturing packets. They observe unicast traffic between internal machines appearing in their packet sniffer—traffic that should have been isolated. What internal switch behavior is responsible for this sudden exposure of isolated traffic?