Palladium-only (with no restrainer) prints can solarize. The blacks can start to lighten with excessive exposure. I have a very nice print that has deeper blacks in the image area than in the blacks in the border area (where the paper is coated beyond the edge of the negative). The base/fog and the little bit of silver in the shadow areas kept the image area blacks from solarizing while the borders began to lighten up.

If this is a problem, adding a little platinum salt prevents the solarization. The platinum in a little NA2 should do the trick, also. I normally print with a 75% Palladium/25% platinum mix. From what I understand, the added platinum will cool your print color down a little, and increase contrast a little. I have been using the 75/25% mix for so long that I have forgotten if that held true for my prints...I also changed paper and developer since I switched to the 75/25% mix, which all affects print color and contrast.