Peter Schätzl Grundwassermodellierer

Streamlines follow the flow field at the current time in the dac file, as if the velocity field would a steady-state field. If you want to trace the flow over a time period, you can use pathlines. See https://en.wikipedia.org/wiki/Streamlines,_streaklines,_and_pathlines for the respective definitions.

An observation point would be one option. Depending on what you want to know, you could also think about doing the statistics over a volume, plot distributions, look at cross-sections, etc.

You'd have to run a transport simulation, marking the water coming from one of the sources by a fake concentration, e.g. 100 mg/l. The concentration in the target area then corresponds to the percentage of the water from the marked source.

Export any elemental property 'As Center' from the data panel.

Also on your bottom slice hydraulic head is zero nearly everywhere - only in a few nodes it is higher. You should definitely check your boundary conditions in this model.

I'd consider a linear add-in for mesh generation, so that you are sure to get edges along the well screen. Depending on the need for precise results, you might also want to somehow control element size around the well.

I agree with Durchlässigkeitsbeiwert - the rate budget is probably the easiest option. In general it would be nice, though, if FEFLOW could - in a future version - show active contraints in a way different from the swapped BC (for example well in case of an active constraint on a head BC) or from just removing the icon (as for the head constraint on transfer BCs).

As said before, I don't think that anyone has experienced something like this before. The basic principle of editing in FEFLOW is that values are changed within the selection for the active parameter(s). Changing more than one parameter at a time is only possible for parameters of the same type (for example the different conductivities). If multiple parameters of different type are active the editor toolbar will even be inactive so that the values cannot be changed.

As answered before, if it was like that it would be clearly a bug. I would recommend, however,  to once again cross-check exactly your steps, as such a severe bug very probably would have been noticed very quickly by many users.

In general, FEFLOW only changes values for a) the active parameter(s) and b) the active selection. If it would change parameter values anywhere else, it would clearly be a but. I would think, however, that this would be something that would be detected and fixed very quickly.