The LoS complications mentioned earlier are correct for all pets that I've used. For example, going through tunnels in PoD causes my necro's pet to run under the ground at times, and his 25k proc won't fire. Same situation happened with walls and corners in BoT.
I imagine classes that do little more than '/pet attack' are the ones that see this issue arise more often than hybrids.
I have never run into that situation, but then again I don't recall any situations beyond my lowbie times on my mage where my pet ran under the ground. I always use /pet hold anytime my pet goes under the ground so maybe that is why? Good to know though. Thanks.