I'm not sure who decided that this was a good feature to not advance the guide while in combat, but I would like to consider it to be removed for the following reasons:

1. Once you are in combat, it sometimes takes a while for you to get out of it. I had to run around around until I was no long in combat to advance to the next step.
2. Sometimes it is necessary to complete a quest and RUN!!!. Most times I end up running in the opposite direction I needed to go and then have to transverse the same mobs to get where I next need to be. So much simpler to just run in the correct direction.

If you can get it working then that'd be great - but this is there because there are restrictions on what can be done in combat. I think this largely revolves around resizing of the window while in combat and with the showing and hiding of the extra buttons in combat. It may be possible to narrow down the changes so that it can still advance, but potentially not update the blocked changes while in combat.

I'm going to try an experiment and turn it off and see how much trouble I get into :-).

Well, its one of those things that works for 90% of the cases and then has bizarre failures for the rest.

I think gameldar is correct and that the problems all revolved around the changing the state of buttons.

So the next hack I'll try is one where buttons updates are suppressed during combat, and if they needed to happen, a flag will be set to redo the display when leaving combat.

The Draenor version of the addon does as much updating as possible within the limits imposed by blizzard.