Thanks for coming back to me. You shouldn't need to get up at 2am because I have found I can reproduce this issue (and others) by navigating future programmes. Also, the programme length does affect this. I checked navigation with an off-air channel that would be on-air in 5.5 hours and this problem did not occur, so that explains why you can't reproduce this on a 4 hour programme. Having tested this further I also get weird behaviour (behavior if you're in the US!) in other circumstances with long running programmes. Full details below. First, in answer to your specific questions:
1. Yes. What I reported occurs with channels that are off air for 12 hours. I have now tested this with 5.5 hours remaining of the off air programme and the issue didn't occur, but with 10 hours remaining it does.
2. Yes, I can navigate through the grid as normal above and below long running programmes. But I can't get "in to" the long running programme from programmes listed in around the first hour of the long running programme's start (or, I have now discovered, it's end).
3. I am using MC 19.0.60 on Windows 7 with Obsidian skin and most of MC has been left at default setup. The TV channels are DVB-T in the UK. I have hidden most TV channels to get rid of all the (1) and (2) repetitions and also to hide the many channels I don't watch. I have also entered channel numbers (these weren't populated when the tuning was performed) and edited all channel names to include the channel number as a prefix, e.g. "1 - ", "2 - ", so that the channels display in the correct order.
Here is a full summary of behaviour I am seeing. "LRP" below means "long running programme" and in my tests this is a 12 hour, off air channel. This list includes further issues but also, I think/hope, clues as to what is happening:
1. When above or below a LRP at the start of the Guide, i.e. far left, the navigation (using arrow keys) won't move to the LRP. Either no navigation occurs or the navigation jumps to the top of the screen and "Guide" is lighted in the topmost menu. If you navigate right in the channel adjacent to the LRP, usually to about 1 hour in the future, then the navigation to the LRP will work.
2. When above or below the start of a LRP in the future, attempting to navigate to that LRP will move the selection to the programme immediately before the LRP. If I navigate in the channel adjacent to the LRP to about 1 hour after the LRP's start then the navigation will correctly move to the LRP. Does this explain the behaviour in issue 1? i.e. MC is trying to navigate to a prior programme and in issue 1 it can't (because we are at the start of the guide) so in that case no navigation occurs? Fix issue 2 and issue 1 will also be fixed?
3. If I navigate to the future and select a programme (in the same channel) immediately before or after a LRP and use the right or left keys to navigate forward or back in time to the LRP, then one of two things happens. Either nothing happens, i.e. no navigation, or the navigation jumps to the top of the screen and "Guide" is lighted in the topmost menu. It is impossible to navigate in to the LRP.
4. I tried navigating to a programme 3 hours long. That didn't have the problems described in 1, 2 & 3. However, if I tried to navigate to that programme from a programme on an adjacent channel that started within the final 1.5 hours of the 3 hour programme, then the navigation jumped to the programme after the 3 hour programme. The navigation should have moved to the three hour programme. The same issue occurs with a LRP, and in that case the problem occurred from any programme that started within the last 3 hours of a 12 hour LRP.
5. When I navigate down the list of programmes in the Guide and get to the last entry, the next press of the down arrow key causes navigation to jump back to the second entry in the list and not the first. This happens with all programmes regardless of length.
I hope that helps you fix this.