We are able to isolate the issue. I have uploaded the sample here: http://1drv.ms/1znQkRX
Please follow the following steps to reproduce the issue:
1) Open ZM.SFA.Tab.All.sln under the All folder. ZM.SFA.Tab.Core project should be the startup project.
2) "C:\Logs\WriteLines.txt" is a file I write to check if virtualization is happening or not. Please create a folder called "Logs" in your C: drive and create a text file with the name "WriteLines.txt".
3) Rebuild the solution in Debug mode.
4) Run the application.
5) Keep the C:\Logs\WriteLines.txt open in Notepad++. Make sure it is empty.
6) Click on the button "NO GROUPING". The C:\Logs\WriteLines.txt will have 15 entries. Even though there are 127 records in the grid, the getter in model is hit only 15 times.
7) Click on the Close (X) button on the tab called "CustSearchHeader".
8) Now clean the C:\Logs\WriteLines.txt file.
9) Now click on the button "GROUPING".
10) You will notice that C:\Logs\WriteLines.txt file has 503 entries. This means Virtualization is not happening.