Transient pathlines starting from a polyline

Hello,
Does anyone have experience plotting transient pathlines originating from a polyline? When I try to do this, only one or two pathlines plot along one end of the polyline, rather than spreading out over the length of the line, and the number of lines do not correspond to the number of starting seeds.  It doesn't seem to make a difference if I choose the flux-weighted distribution option or not, and although my darcy flux is low, it is not zero.  Has anyone seen this before, and could you tell my why in theory this could happen?

Thanks!

One possibility where such a behavior can occur is when you choose the wrong direction for the pathlines. For example, starting backward pathlines on the top slice of a model with groundwater recharge will typically not result in long lines, they may even be completely invisible as the velocity vectors point upwards out of the model.

Hi Peter,
Thanks, yes that possibility makes sense.  However I am doing forward tracking starting in the top slice with groundwater recharge, and one node will plot for hundreds of meters in the first slice, but the adjacent node does not plot at all.  It seems to me the vertical gradients should not be different enough to drive one particle down to slice 2 immediately, whereas the other particle remains in the top slice, particlularly if K, recharge, and BCs are not very different in the immediate area.

Another question - As I understand it, If I chose a timestep to view in the postprocessor, then run (say in this case, forward) particle tracking, the particle tracks start at the timestep I am currently in, and run until the end of the simulation ( in my case, the model starts at 0 days, I start the particles at 10 days and they run until the end of the model at 30 days).  I only want to view the particle trace from 10 to 20 days, however.  So I go to the properties of the pathlines and have the option to change the minimum and maximum time to plot (via the color bar).  The minimum is always the start time of the model and the maximum is always the end of the simulation.  When I turn off the "autorange" and change the minimum to 10 and the maximum to 20, no particles plot.  When I change the minimum to 0 and the max to 20, the particles plot again.  This doesn't make much sense to me!  Does this mean that no matter what timestep I am currently in, the model is always plotting particles from time step 0 to time step 30? 

Thanks for you help, I need to understand this so that my pathlines make sense!