Changed appearance streams weren't marked as modified. SUP-1942

Author: michaeldemey

forms/src/main/java/com/itextpdf/forms/fields/PdfFormField.java

@@ -86,8 +86,6 @@ This file is part of the iText (R) project.
 import com.itextpdf.layout.property.Property;
 import com.itextpdf.layout.property.TextAlignment;
 import com.itextpdf.layout.property.VerticalAlignment;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
@@ -96,6 +94,9 @@ This file is part of the iText (R) project.
 import java.util.List;
 import java.util.Set;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
 /**
  * This class represents a single field or field group in an {@link com.itextpdf.forms.PdfAcroForm
  * AcroForm}.
@@ -1911,6 +1912,7 @@ public boolean regenerateField() {
                 appearance.getResources().addFont(getDocument(), localFont);
                 PdfDictionary ap = new PdfDictionary();
                 ap.put(PdfName.N, appearance.getPdfObject());
+                ap.setModified();
                 put(PdfName.AP, ap);
 
                 return true;