How to reproduce: Create a DPI-aware application and run it on a Windows 10 machine on 125%, the text inside the editors is smaller compared to the text in cells which are not in edit mode.

Workaround: 
private void RadGridView1_CellEditorInitialized(object sender, GridViewCellEventArgs e)
{
    BaseInputEditor editor = e.ActiveEditor as BaseInputEditor;

    if (editor != null)
    {
        RadTextBoxItem item = editor.EditorElement.FindDescendant<RadTextBoxItem>();

        if (item != null)
        {
            item.HostedControl.Font = this.radGridView1.GridViewElement.GetScaledFont(this.radGridView1.GridViewElement.DpiScaleFactor.Height);
        }
    }
}