off the shelf switch can introduce a loop into network

Every so often, an off the shelf switch (netgear, trendnet, etc) manages to cause a loop in the network - an L2 Cisco network comprised of various Catalyst switches. I have bpduguard and loopguard in place everywhere. Trunk ports between switches will shutdown because a loop is detected. These off the shelf switches are merely just plugged in to one port, just their presence is all that it takes - they are not wired to create a loop (plugging in two wall jacks to two ports on the switch). I dont have broadcast or storm control enabled. I'm just curious what protections it takes to prevent a malfunctioning rogue off the shelf switch from drastically degrading the network. Any ideas, what have I missed?

thanks....