The UNKNOWN(3) mip selection mode seems to act like CONST. Keep that working.

GPU/Common/TextureCacheCommon.cpp

@@ -228,6 +228,7 @@ void TextureCacheCommon::UpdateSamplingParams(TexCacheEntry &entry, SamplerCache
 				break;
 			}
 		case GE_TEXLEVEL_MODE_CONST:
+		case GE_TEXLEVEL_MODE_UNKNOWN:
 			key.maxLevel = (int)(lodBias * 256.0f);
 			key.minLevel = (int)(lodBias * 256.0f);
 			key.lodBias = 0;

GPU/ge_constants.h

@@ -417,6 +417,7 @@ enum GETexLevelMode {
 	GE_TEXLEVEL_MODE_AUTO = 0,
 	GE_TEXLEVEL_MODE_CONST = 1,
 	GE_TEXLEVEL_MODE_SLOPE = 2,
+	GE_TEXLEVEL_MODE_UNKNOWN = 3,  // Behaves like CONST.
 };
 
 enum GEMaterialColorSetting