publishing two hidden services descriptors to the same relay will use the same circuit
#5283 (moved) made me notice another fun side effect: if your Tor operates two hidden services, and they happen to pick overlapping hsdir points, and happen to publish somewhat nearby in time, the descriptor publishes will share the same circuit, linking the hidden services together from the perspective of the hsdir.
A less dangerous variation of this issue is when you visit a hidden service whose hsdir is the same as the hsdir chosen by the hidden service you offer.