Version 2016.3.1024.45 (from nuget packages, if that matters)
Adding a new row with the "Add new row" button and then clicking the row indicator results in an extra row. Demo: http://recordit.co/Nn8y2z2YpI

Available in the R1 2017 SP1 Release.

An exception with the following StackTrace is thrown:

       at System.Windows.Threading.Dispatcher.VerifyAccess()
       at System.Windows.DependencyObject.GetValue(DependencyProperty dp)
       at Telerik.Windows.Data.FilterDescriptor`1.get_FilteringExpression()
       at Telerik.Windows.Data.FilterDescriptor`1.CreateFilterExpression(ParameterExpression parameterExpression)
       at Telerik.Windows.Data.FilterDescriptorBase.CreateFilterExpression(Expression instance)
       at Telerik.Windows.Data.Expressions.FilterDescriptorCollectionExpressionBuilder.CreateBodyExpression()
       at Telerik.Windows.Data.Expressions.FilterExpressionBuilder.CreateFilterExpression()
       at Telerik.Windows.Data.QueryableExtensions.Where(IQueryable source, CompositeFilterDescriptorCollection filterDescriptors)
       at Telerik.Windows.Data.QueryableCollectionView.CreateView()

Available in LIB version: 2017.2.529

Available in LIB version 2017.1.213 , it will be also available in the R1 2017 SP1 Release.

A workaround for the issue is to apply a 1px top Margin.

Available in R3 2017 Release

A workaround for the issue is to use RadObservableCollection as a source collection. Before the items are added to it, call the its SuspendNotifications method. Respectively, after that call the ResumeNotifications one. 

Another approach would be to populate the items through the AddRange method of the collection.

To work this around you can set the EnableColumnGroupsVirtualization to False.

Alternatively you can change the FrozenColumnCount before adding the columns, and reset it once the process is done. For example:

gridTriffDetails.FrozenColumnCount = 0;
 
gridTriffDetails.Columns.Add(newColumn);
gridTriffDetails.Columns.Add(newColumn1);
gridTriffDetails.Columns.Add(newColumn2);
 
gridTriffDetails.FrozenColumnCount = 1;

Currently the new item's properties are validated before editing their values, which is not intuitive, especially for Required, MinLength etc. The correct behavior would suggest that validation should be applied only to "confirmed" property values.