I've done our local Parkrun three times now. I use Endomondo on my phone to time/measure it (and it adds the calories I've burned into My Fitness Pal, so I get to eat more!), but it consistently comes up as over 5k. Almost 5.5 in fact.
There re are quite a few trees, and looking at the map of my run it does have me running off the path at times, so I suppose it could be wrong, but I assume it's correct when I run elsewhere.
So, am I running more than 5k, or does it mean that when I'm running elsewhere and I think I've done 5k, I haven't?