In D3D9 no problems occur, however in both D3D10 and 11 (tested in Crysis (DX10) and Postal 2 (DgVoodoo2 D3D8-to-D3D11)), the following happens after blurring (for bloom):
From some testing, I've come to the conclusion that due to some sort of compiler error, dark pixels sometimes go negative, which in turn glitches out the bloom effect done afterwards.
Simply using max(0, col) (after hsv2rgb(col)) fixes this completely, as shown below:
As far as I know that simple fix seems to do the trick and no other problems seem to occur from this specific case.
Here are two more screenshots showing only the bloom effect itself for the sake of completely demonstrating the problem:
So far I have only seen this problem in 3.0, including the beta and final versions, I haven't tested it in 2.0.