Created Unassigned: Use DockHeight auto in a nested LayoutPanel causes an exception [20747]

I attached a sample application to reproduce the unexpected behaviour.

Following steps to reproduce the exception:

1. Start the sample program
2. Move the grid splitter down over the listbox titled with "validation"
3. An excpetion is thrown at:
System.ArgumentException was unhandled
HResult=-2147024809
Message='-48' is not a valid value for property 'Height'.
Source=WindowsBase
StackTrace:
at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
at System.Windows.Controls.RowDefinition.set_Height(GridLength value)
at Xceed.Wpf.AvalonDock.Controls.LayoutGridControl`1.OnChildModelPropertyChanged(Object sender, PropertyChangedEventArgs e)
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