Hello,

You have to specify the field with lowercase in the column definition. Here's the updated example:
http://dojo.telerik.com/EReJO/6

Regards,
Bozhidar
Telerik

Unfortunately this is not acceptable solution. Each data source item has fields (properties of the object) "title" (from Kendo default schema) and "Title" (from user fields). Since java script is case sensitive those fields represent different properties. There can be many other user fields ("Description", "ReminderDate", "TaskCost", etc.) and they are not intersect default kendo fields like "title", "start", "end", etc. What if I do not want do display default task title. I provide custom columns array without "title" field and get the same incorrect behaviour with summary tasks. Link with the example. Nothing is written in the documentation that "title" field is required field in the "columns" array.

Since Kendo Gantt requires at least one column to be displayed I guess that correct behaviour with displaying summary tasks should be the following: display triangle (which expands children tasks) in the first table column (even if the first field in the columns array is not "title"). Can be such behaviour achieved in the latest (2014.3.1411) version? 

Unfortunately this is not acceptable solution. Each data source item has fields (properties of the object) "title" (from Kendo default schema) and "Title" (from user fields). Since java script is case sensitive those fields represent different properties. There can be many other user fields ("Description", "ReminderDate", "TaskCost", etc.) and they are not intersect default kendo fields like "title", "start", "end", etc. What if I do not want do display default task title. I provide custom columns array without "title" field and get the same incorrect behaviour with summary tasks. Link with the example. Nothing is written in the documentation that "title" field is required field in the "columns" array.

Since Kendo Gantt requires at least one column to be displayed I guess that correct behaviour with displaying summary tasks should be the following: display triangle (which expands children tasks) in the first table column (even if the first field in the columns array is not "title"). Can be such behaviour achieved in the latest (2014.3.1411) version? 

Hello,

The title field is indeed not required, however the expand/collapse and tree-like display where the child items are offset to the right it bound only to the column representing the "title" field of the gantt datasource schema. Currently there is not way to change this behavior, but we will research how we can enable it in the future.

Regards,
Bozhidar
Telerik