DBSCAN flaws

[notnot]

DBSCAN Guesses() can sometimes return indices of -1. Not supposed to happen i guess?
Besides that, there seems always to be a cluster with just one point as the last entry. This point does not need to be an outlier at all, it often is located somewhere inside another cluster!

---- edit -----

I now understand that -1 probably means an outlier point, not belonging to any cluster. These points are often situated inside clusters though, so why are then not assigned to that cluster?