Sunrise and Sunset widget gone whacky. F5x version 15.4

Just recently I had reason to check on when it was going to get dark whilst I was out on a run, so I pulled up the sunrise/sunrise widget on the F5x and imagine my surprise to find that it looked like this                       

I had apparently been transported to a place where Sunset was around 12:25 oclock-ish. With Sunrise only an hour and a bit beforehand. I dunno where this place is, really far north or south, I imagine, but it ain't Melbourne Australia!

I checked that it was using 'current location ' instead of some bogus coordinates and I had a recent correct GPS fix because I was using the GPS to track myself during the run. I dicked around with button pressing for a while (it was nice to have a break from the run, and given that I had until midnight before the sun was going to set, there was no sense of urgency, tho strangely, it was starting to get dark around the 8:30 pm mark...)

Eventually, as if by magic, the sunset time suddenly changed to 8:30 pm. (Aha!) and it stayed consistent with reality for a few times after that whenever I chose to check it. I passed it off as an update glitch. (I first noticed this just after the recent 15.4 update)

But now it is back again and didn't appear to be going to correct itself.  Actually it did but it took a considerable time, I fiddled with it for 30 mins or more before giving up in disgust. When I looked at it again after another 30 min break it was correct at 8:19pm)

What the &*#$@#$(&*^& is the good of this thing? Twice in a row it let me down when I needed it. If I am out on the tracks and in danger of getting benighted, do I have to wait for an hour to find out when the sun is going to set? I'd be able to tell by then because it'd have gotten dark!

Anyone else having similar issue? Is this 'normal'? could have sworn it used to work OK, but am not sure.