autoGenerate and noFormPost are required for JSON fields. Fixes bug #10991.

docs/changelog/7.x.x.txt

@@ -39,6 +39,7 @@
  - fixed #10913: User profiles: Impossible to delete field contents
  - fixed #10929: EMS Ticket Start Date Sort
  - fixed #10885: Code Editor breaks Javascript comments
+ - fixed #10991: Calendar: bug in Display tab
 
 7.7.19
  - fixed #10838: Forwarded forum post email to new CS adds reply to original thread

lib/WebGUI/Asset/Wobject/Calendar.pm

@@ -261,6 +261,7 @@ sub definition {
             defaultValue    => [],
             serialize       => 1,
             noFormPost      => 1,
+            autoGenerate    => 0,
             tab             => "display",
         },