I have an HDHomeRun (HDHR t1 us), and this device only has one usable tuner, though LMCE detects 2. I presume the second is some sort of fake to allow recording one thing and watching another. I have a couple of crap cards that do the same thing, though I know there is only one usable tuner. Snapshot 22982 (or later) with the MythTV .23 shoehorn prioritizes the fake tuner and will not access the correct one before crashing. Deleting the tuners and redefining the single usable tuner gets overwritten as soon as the changes are applied (presumably after mythfilldatabase is run).
In order to prevent this, or more accurately allow your changes in MythTV Setup to be applied and not overwritten, in the web admin drop to device tree/Core/DCERouter/Myth TV Plugin. Towards the bottom of the page is a checkbox which says "Dont autoconfigure"
Then delete all, define card/input, and when it says mythtv is ready... it is. I am sure many of you are already aware of that checkbox... but it cost me almost 2 days... so naturally I think it's discovery is like finding Atlantis. Hope this helps someone having troubles.