I have been using a virtual grid for some time and kept getting odd issues with it. I have finally managed to get it down to a minimal case to reproduce the issue. It looks like the grid is truncating part of the numbers that I am using to index into another database.
The attached program demonstrates the problem - selecting "testfield" from the combobox dropdown does not display the proper value for the DisplayMember. It is also not possible to navigate to that using the keyboard, it can only be selected via the mouse.
gridtest5.zip