fixed filtering of used declarations when a vendor prefix is present

lib/single-file/modules/css-matched-rules.js

@@ -287,7 +287,9 @@ this.matchedRules = this.matchedRules || (() => {
 				const declarationInfo = declarationsInfo.get(declarationData);
 				if (!declarationInfo || (declarationData.important && !declarationInfo.important)) {
 					declarationsInfo.set(declarationData, { selectorInfo, important: declarationData.important });
-					processedProperties.add(declarationData.property);
+					if (!declarationText.match(REGEXP_VENDOR_IDENTIFIER)) {
+						processedProperties.add(declarationData.property);
+					}
 				}
 			}
 		}