As mentioned
in this post
the developer is divided into two parts as a stock solution. Part B is the
larger quantity of the two and suffers from settlement where the powder comes
out of suspension and accumulates at the bottom of the bottle. Before use, you
should shake the bottle well so that it goes back to a milky colour. It would
seem that the larger the crystals in packet B the more drop out there will be.
I have not yet found a method that stops this.