The bug can be reproduce with the configuration as in the screenshot:
From above the lanes come from an asteroid that produces blue shapes. The red asteroid is feeding into the same lanes for its output, so far no problem.
Now the blue lane is split out and onto the red-shape platform where I simply attached an open ended belt. Its preview blinks between the blue shape that is there and the red shape that is being fed into the same lane, but impossible to receive on that output because it feeds further "downstream".
