When merging a PDF with form fields (page2.pdf) to a PDF generated via FOP (page1.pdf), the form fields of page2.pdf are not shown in the result in Acrobat Reader.
When merging page2.pdf twice, the form fields are not shown for the first occurrence but are shown for the second occurrence.
When merging page2.pdf with a PDF created by MS Word, the problem is not reproducible.
Command line to reproduce the problem:
java -classpath pdfbox-app-1.8.4.jar org.apache.pdfbox.PDFMerger page1.pdf page2.pdf page2.pdf result.pdf