I have the same experience when mixing D-76 – Little particles that float around for a while, but if I let it sit for a day, then they disappear, and everything works fine.(posted 8207 days ago)I just bought a new gallon package of D-76, and there are new instructions. It does state to start with 800ml of hot water, which differs from the old instructions, which called for a larger amount to start with. I tried the smaller amount, and it worked fine. I am not sure why Kodak changed their instructions.
Good luck!