Index: lib/filterClasses.js
===================================================================
--- a/lib/filterClasses.js
+++ b/lib/filterClasses.js
@@ -122,17 +122,17 @@
   let filter = Filter.knownFilters.get(text);
   if (filter)
     return filter;
 
   let match = text.includes("#") ? Filter.contentRegExp.exec(text) : null;
   if (match)
   {
     let propsMatch;
-    if (!match[2] &&
+    if (!match[2] && match[3].includes("[-") &&
         (propsMatch = /\[-abp-properties=(["'])([^"']+)\1\]/.exec(match[3])))
     {
       // This is legacy CSS properties syntax, convert to current syntax
       let prefix = match[3].substr(0, propsMatch.index);
       let expression = propsMatch[2];
       let suffix = match[3].substr(propsMatch.index + propsMatch[0].length);
       return Filter.fromText(`${match[1]}#?#` +
           `${prefix}:-abp-properties(${expression})${suffix}`);