Example image attached shows the issue.
To work around that weirdness(bug?) you have to subdivide it a few times before projecting.
(which is a huge pita and makes editing the mesh after projection a huge undertaking).
Maya doesn't suffer from this for example.
Andrew Price (blenderguru) noticed that behaviour with v.2.66 https://www.youtube.com/watch?v=B9r9tKX5olY&t=1321 so i guess this issue is there since a long time.