Wpf flowDocument处的打印问题'；s内部复选框

我想知道这是否是打印flowdocument的正确方法：（ 但这是一个非常奇怪的现象

我的代码如下：

string flowDocString =
" <FlowDocument xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'>" +
"      <Section>" +
"          <Paragraph>" +
"              <CheckBox IsChecked='True'>Test</CheckBox>" +
"          </Paragraph>" +
"      </Section>" +
" </FlowDocument>";
FlowDocument flowDoc = (FlowDocument)XamlReader.Load(new MemoryStream(new UTF8Encoding().GetBytes(flowDocString)));

PrintDialog printDlg = new PrintDialog();
IDocumentPaginatorSource idpSource = flowDoc;
printDlg.PrintDocument(idpSource.DocumentPaginator, "Hello WPF Printing.");

string flowDocString =
" <FlowDocument xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'>" +
"      <Section>" +
"          <Paragraph>" +
"              <CheckBox IsChecked='True' IsEnabled='False'>Test</CheckBox>" +
"          </Paragraph>" +
"      </Section>" +
" </FlowDocument>";

string-flowDocString=
" " +
"      " +
"          " +
“测试”+
"          " +
"      " +
" ";
FlowDocument flowDoc=（FlowDocument）XamlReader.Load（新的MemoryStream（新的UTF8Encoding（）.GetBytes（flowDocString））；
PrintDialog printDlg=新建PrintDialog（）；
IDocumentPaginatorSource idpSource=flowDoc；
printDlg.PrintDocument（idpSource.DocumentPaginator，“Hello WPF Printing.”）；

当我使用这段代码时，复选框的状态仍然是未选中的。 但是当我像这样修改flowDocString时：

string flowDocString =
" <FlowDocument xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'>" +
"      <Section>" +
"          <Paragraph>" +
"              <CheckBox IsChecked='True'>Test</CheckBox>" +
"          </Paragraph>" +
"      </Section>" +
" </FlowDocument>";
FlowDocument flowDoc = (FlowDocument)XamlReader.Load(new MemoryStream(new UTF8Encoding().GetBytes(flowDocString)));

PrintDialog printDlg = new PrintDialog();
IDocumentPaginatorSource idpSource = flowDoc;
printDlg.PrintDocument(idpSource.DocumentPaginator, "Hello WPF Printing.");

string flowDocString =
" <FlowDocument xmlns='http://schemas.microsoft.com/winfx/2006/xaml/presentation'>" +
"      <Section>" +
"          <Paragraph>" +
"              <CheckBox IsChecked='True' IsEnabled='False'>Test</CheckBox>" +
"          </Paragraph>" +
"      </Section>" +
" </FlowDocument>";

string-flowDocString=
" " +
"      " +
"          " +
“测试”+
"          " +
"      " +
" ";

如果修改，上述结果将按预期显示。 怎么会这样？请告诉我为什么