Multigraph not showing details

I have noticed that recently, the multigraph on my dashboard has been behaving strangely.  I think this is new in the last few weeks.

Have a look here: emoncms.org/engeeaitch  The light blue section shows when the boiler has been turned on or off.  The default view shows the data for a week - and this suggests that the boiler has been on permanently since 28 September (it hasn't!).  On selecting the daily view, you can see that it has only been on for about 20 minutes today, and scrolling to the left, shows that it was not on at all yesterday (1 October).  On the weekly view,  I would have expected just a small spike today (or perhaps nothing at all if it was only on for a very short period) and nothing for yesterday. (Note - there was some data lost at the start of today - that was a different issue).

Any ideas why this should be?

For the boiler feed, I send a 1 when the boiler is on, and a 0 when it is off (the input is multiplied by 5 for sending to the feed, so that the multigraph is scaled sensibly).  This is repeated every 10 minutes.  The only thing that I can think of that has changed is that when the boiler changes state, I now send the current state followed by the new state - so that the feed which captures the time that the boiler has been on for is more accurate.