I'm pretty sure I've read on here that Calibre relies on the users of this fantastic free software to do a lot of the testing. That's a small price to pay for what we are all getting here. We are so lucky to have Calibre with its current development/testing model as it exists. Sometimes it can be tough to be an open source developer as the users often end up taking things for granted and forgetting that this is done as a hobby in someone's own time for free.
Keep up the great work Kovid!!