Fixed checking for no support for user flags

app/src/main/java/eu/faircode/email/Core.java

@@ -5210,11 +5210,13 @@ class Core {
 
             if (!Helper.equal(message.keywords, keywords) &&
                     !folder.read_only &&
-                    (ifolder.getPermanentFlags().contains(Flags.Flag.USER) || keywords.length > 0)) {
+                    (ifolder.getPermanentFlags().contains(Flags.Flag.USER) || MessageHelper.hasUserKeywords(keywords))) {
+                Log.i(folder.name + " updated id=" + message.id + " uid=" + message.uid +
+                        " flags=" + ifolder.getPermanentFlags().contains(Flags.Flag.USER) +
+                        " keywords=" + (message.keywords == null ? null : TextUtils.join(" ", message.keywords)) +
+                        "/" + TextUtils.join(" ", keywords));
                 update = true;
                 message.keywords = keywords;
-                Log.i(folder.name + " updated id=" + message.id + " uid=" + message.uid +
-                        " keywords=" + TextUtils.join(" ", keywords));
 
                 message.importance = null;
                 for (String keyword : keywords)

app/src/main/java/eu/faircode/email/MessageHelper.java

@@ -302,6 +302,13 @@ public class MessageHelper {
             "$social" // mailbox.org
     ));
 
+    private static final List<String> FLAG_USER = Collections.unmodifiableList(Arrays.asList(
+            FLAG_CLASSIFIED,
+            FLAG_FILTERED,
+            FLAG_LOW_IMPORTANCE,
+            FLAG_HIGH_IMPORTANCE
+    ));
+
     // https://tools.ietf.org/html/rfc4021
 
     static void setSystemProperties(Context context) {
@@ -1591,6 +1598,22 @@ public class MessageHelper {
         return true;
     }
 
+    static boolean hasUserKeywords(String[] keywords) {
+        if (keywords == null)
+            return false;
+        for (String keyword : keywords) {
+            if (TextUtils.isEmpty(keyword))
+                continue;
+            if (FLAG_USER.contains(keyword))
+                return true;
+            if (FLAG_BLACKLIST.contains(keyword))
+                continue;
+            if (!keyword.startsWith("$"))
+                return true;
+        }
+        return false;
+    }
+
     String getMessageID() throws MessagingException {
         ensureEnvelope();