SytaxEditor MouseUp, MouseLeftButtonUp doesn't trigger

My code is

<editor:SyntaxEditor x:Name="editor"  Grid.Row="0" AreLineModificationMarksVisible="False"  
                MouseMove="Editor_MouseMove" MouseDoubleClick="Editor_MouseUp" MouseRightButtonUp="Editor_MouseRightButtonUp" 
                FontSize="14" Text="{Binding FormulaString, Mode=OneTime}"
                WordWrapMode="Word" HorizontalScrollBarVisibility="Hidden" CanSplitHorizontally="False"
                     DocumentTextChanged="Editor_DocumentTextChanged" 
                     UserInterfaceUpdate="OnEditorUserInterfaceUpdate" />

private void Editor_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)
{
    ...      
}

private void Editor_MouseUp(object sender, MouseButtonEventArgs e)
{
    ...      
}

private void Editor_MouseRightButtonUp(object sender, MouseButtonEventArgs e)
{
    ...      
}

The MouseUp Event does not trigger. I tried MouseLeftButtonUp and it does not work neither. However others like MouseMove, MouseRightButtonUp and MouseDoubleClick are fine. Are these two events still available? If so, how could the two events disabled? This is a legacy project I am migrating. I am not very familiar with the ActiPro.