When you set a programme to be recorded, it seems like you have very little control over what gets recorded, and when.
I thought I'd set a recording for the Great British Bake Off, but instead of recording first broadcast of the next episode, on Channel 4, the box opted for a repeat later in the week. Now I have it recording correctly, but after I've watched an episode, I also seem to get repeats recorded anyway. Other programmes get the same treatment. I watch and then delete a recording, and the box records a later repeat. I've no idea why.
One gotcha I spotted is if you search for a show then click on a result in the search, you go to a sort of info screen for the series. You might, or you might not, be taken to a page for the HD broadcast of that show, particularly if it's a BBC show, where it might be offering you BBC One, BBC One HD, BBC Wales, BBC Northern Ireland... I try to make sure I'm at least starting out on the right channel, but whether that means the channel I want will be recorded or not, I don't know.