The table defined in the module portrait for the class icons has a wrong entrie for the deathknight.
The correct entrie would be
["DEATHKNIGHT"] = {0.25, 0.49609375, 0.5, 0.75},
or as complete table:
local classIcons = {
    ["WARRIOR"] = {0, 0.25, 0, 0.25},
    ["MAGE"] = {0.25, 0.49609375, 0, 0.25},
    ["ROGUE"] = {0.49609375, 0.7421875, 0, 0.25},
    ["DRUID"] = {0.7421875, 0.98828125, 0, 0.25},
    ["HUNTER"] = {0, 0.25, 0.25, 0.5},
    ["SHAMAN"] = {0.25, 0.49609375, 0.25, 0.5},
    ["PRIEST"] = {0.49609375, 0.7421875, 0.25, 0.5},
    ["WARLOCK"] = {0.7421875, 0.98828125, 0.25, 0.5},
    ["PALADIN"] = {0, 0.25, 0.5, 0.75},
    ["DEATHKNIGHT"] = {0.25, 0.49609375, 0.5, 0.75},
}

Currently it displays the paladin icon.