iBooks is changing my PDF file names in the library list

I have come across an irritating problem with using iBooks to view PDF files on an iPad2. I needed to refer to dozens of documents (court evidence) and so copied the PDFs into a folder and changed the filenames top match the "exhibit" numbers. Then I dragged the files onto the iTunes Library window and they successfully imported into iTunes. Next I synchronised the iPad2 and chose the PDFs. All well and good - the list of PDFs displayed in the iPad library, using the file names that I had assigned.

However when I viewed a PDF with iBooks and returned to the library list the file name had changed to the something embedded in the PDF (maybe metadata or the orginal file names?). This made my list very difficult to use. The only saving grace was that the original order of the documents was retained.

I will report this to Apple iBooks feedback but wondered if others had encountered this bug.

(iPad ios5)