NavMesh doesn't seem to produce the shortest path

Hello,

I've been trying some simple tests with NavMesh and I am seeing some strange artefacts:


Grey objects are obstacles and red lines is the path produced via NavMesh.CalculatePath. As you can see the red path is not the shortest path from srs to dust. Interestingly sometimes if I try a path from dst to src (i.e. swapping dst and src) it may produce the shortest one. Is this the expected behaviour or am I missing something? Thanks.