DC electronic load BK8500 oscillations in CR mode, not broken but bad design.

[Rufus]

The load does not know which solution to use.

The load controls resistance of the pass MOSFETS in a feedback loop. The polarity of the required feedback changes depending which side of maximum power transfer you are. I doubt the load bothers trying to support the case were the source resistance is higher than the required load resistance.

[MarkL]

The load does not know which solution to use.

The load controls resistance of the pass MOSFETS in a feedback loop. The polarity of the required feedback changes depending which side of maximum power transfer you are. I doubt the load bothers trying to support the case were the source resistance is higher than the required load resistance.

That seems to be the case; I don't see any options in the manual.  There are some loads where you can set which side of the curve (I or V) to approach the power set point.