Recently we have reviewed this item and would like to inform you that with the current implementation of RadGridView's Focus method the observed by you behavior is an expected one.
The issue in not directly connected with the IsSynchronizedWithCurrentItem property. It could be observed and reproduced if the MoveCurrentToLast method is called for the Items collection of RadGridView before calling the Focus method. For such scenarios we recommend MoveCurrentToLast to be called after the Focus method. Also, for scenarios where the SelectedItem is set before Focus it is recommended Focus to be called first. The Focus method depends on the CurrentCell of the GridView and if it does not have such it makes the first cell of the first row CurrentCell. So, if it is called after MoveCurrentToLast a new CurrentCellInfo will be created (which will be the first cell in the firs rowt) and when BeginEdit gets called it is expected to edit that first cell using the created in the Focus method CurrentCellInfo.
Please, check the attached sample project that demonstrates how we recommend using Focus with IsSynchronizedWithCurrentItem.