Same here, never been a problem to disconnect anytime as long as it is not transferring recordings to or fro. However, I do one thing just to play it a bit safe: The drive I use (the WD's) will spin down after several minutes. Once I have finished using the HDD, I'll wait about 10 minutes, (which I've noticed is usually the time by which the HDD needs to "wake up" or spin up to start responding to commands), and by then the HDD has spun down, and then I disconnect at that time or beyond, while it's "sleeping" or a nappin.
I've disconnected HDD's even before spin down and still no problems. I think the OP does have a problem with the Hopper itself. However, I would recommend to anyone to wait long enough for spin down for the HDD and then disconnect. Disconnecting the DVR is just plain crazy and has a chance of breaking the DVR if it is writing, and we never really know when the DVR is writing data, so it's a crap shoot. The DVR's reboot every night as it is; excessive rebooting just brings the device closer to death.