It's definitely possible and I've seen way to much beer dumped because of it. Our issue was Acetaldehyde, not diacetyl, but same principal of stratification in the tank. The easy/expensive fix is upping the HP of your k/o pump. Eventually we did that. It was simply undersized for the length of the draw to newer tanks, which is where all the issues were (placed further away from the brew-house). The cheap fix, which for the most part eliminated our problem was flipping the racking arm up to about 10 o'clock, and then knocking out the 2nd, 3rd, and 4th brews through the racking arm. That mixes the wort in the tank up better so stratification isn't an issue. Double valve it so you canm do it sanitarily. We also started to pitch yeast on the first and third k/o rather than all in the first. Like I said, we only had issues in tanks that were far away from the brewhouse, so I believe the underlying issue was an undersized k/o pump. Also check into your yeast health, and whether you are over-oxygenating, under-oxygenating, giving to many nutrients, etc. I also spent alot of time checking the yeast count at every k/o, the DO levels, etc. to make sure everything was looking good. Hope that helps.
edit: also look at your yeast strain. it may be floccing out of the top third of the tank too quickly to re-absorb the diacetyl, but has enough contact time with the rest of the tank to have no issues.