Added (slightly modified) patch from #2806

ActiveSync/SOGoMailObject+ActiveSync.m

@@ -761,7 +761,7 @@ struct GlobalObjectId {
   
   // Flags
   [s appendString: @"<Flag xmlns=\"Email:\">"];
-  [s appendFormat: @"<FlagStatus>%d</FlagStatus>", 0];
+  [s appendFormat: @"<FlagStatus>%d</FlagStatus>", ([self flagged] ? 2 : 0)];
   [s appendString: @"</Flag>"];
   
   // FIXME - support these in the future
@@ -799,10 +799,21 @@ struct GlobalObjectId {
 
   if ((o = [theValues objectForKey: @"Flag"]))
     {
-      o = [o objectForKey: @"FlagStatus"];
-      
-      if ([o intValue])
-        [self addFlags: @"\\Flagged"];
+      // We must handle empty flags -> {Flag = ""; } - some ActiveSync clients, like the HTC Desire
+      // will send an empty Flag message when "unflagging" a mail.
+      if (([o isKindOfClass: [NSMutableDictionary class]]))
+        {
+          if ((o = [o objectForKey: @"FlagStatus"]))
+            {
+              // 0 = The flag is cleared.
+              // 1 = The status is set to complete.
+              // 2 = The status is set to active.
+              if (([o isEqualToString: @"2"]))
+                [self addFlags: @"\\Flagged"];
+              else
+                [self removeFlags: @"\\Flagged"];
+            }
+        }
       else
         [self removeFlags: @"\\Flagged"]; 
     }

NEWS

@@ -6,7 +6,7 @@ Enhancements
  - implemented the GetAttachment ActiveSync command (#2808)
 
 Bug fixes
-
+ - better handling of empty "Flag" messages over ActiveSync (#2806)
 
 2.2.5 (2014-06-05)
 ------------------

SoObjects/Mailer/SOGoMailObject.h

@@ -114,6 +114,7 @@ NSArray *SOGoMailCoreInfoKeys;
 - (NSException *) removeFlags:(id)_f;
 
 - (BOOL) isNewMail;  /* \Recent */
+- (BOOL) flagged;    /* \Flagged */
 - (BOOL) read;       /* \Unseen */
 - (BOOL) replied;    /* \Answered */
 - (BOOL) forwarded;  /* $forwarded */

SoObjects/Mailer/SOGoMailObject.m

@@ -1464,6 +1464,11 @@ static BOOL debugSoParts       = NO;
   return [self _hasFlag: @"seen"];
 }
 
+- (BOOL) flagged
+{
+  return [self _hasFlag: @"flagged"];
+}
+
 - (BOOL) replied
 {
   return [self _hasFlag: @"answered"];