Why does NavMesh Agent pause when I go up stairs

Hi,

I have a strange problem, when I run around the NaveMesh Agents follows me but if I go up or down any stairs, ladders the NaveMesh Agents pause for around a second before chasing me up or down the stairs, ladders as if they are working out the best route to me, should this happen or is something going on?

Thanks.

It is most likely calculating the shortest path too you.