Symptoms
GetList method does not work against Task List - Summary Task smart object of both SharePoint Service V2 and SharePoint Content service instance types.
Reproduction steps:
Create a new list of Tasks List type in SharePoint 2010 and add some items. This list template includes two content types - Task and Summary Task, create couple of items of each type for this test.
Then, create SharePoint Service V2 service instance for this list and smart objects from it. Task List - Tasks and Task List - Summary Task SmartObjects can be created out of it.
Next, execute GetList method for Task List - Summary Task SmartObject - it will not return anything, but Load method of Task List - Summary Task SmartObject returns items of both Task and Summary Task types. GetList method for Task List - Task, works returning only items of Task type.
Diagnoses
SharePoint V2 service broker was initially designed for SharePoint 2007 and consequently it has some issues/limitations when working against SharePoint 2010. For SharePoint Content service broker, which was designed for SharePoint 2010 everything is expected to work correctly, but this particular functionality does not work in 4.6.8.
Resolution
There is a coldfix for this issue for 4.6.8 which can be obtained through K2 support. This coldfix addresses aforementioned issue with SharePoint Content service broker and contains updated version of SourceCode.SharePoint.Client.dll.