If your grid keeps selection after reload then list of records obtained by grid.getSelectionModel().getSelection() contains the same records before and after reload, so if some selected records have been changed you'll never find it until deselect and then selecte records again.
Steps to reproduce the problem:
Select a record in grid, change some field in the same record, after update reload store and them console.log in the selection record. the selected record is still the old one, You need to unselect and select again to see changes made
The result that was expected:
the selected recors keep unchanged
The result that occurs instead:
When you update some field in record, the selection reference needs to be also updated