Hi!
I don't have access to devart TVirtualTable, but I've run before into this 7-8 rows issue when using LoadAllDataAndDisconnect. I was using BlockReadSize in my Dataset, so it behaves someway that is not "compatible" with the grid's db adapter & LoadAllDataAndDisconnect.
Maybe you could try change some properties of your VirtualDataset, or test your program using a "native" dataset and see if it works.